Geode Cake Tutorial

About This Geode Cake Tutorial

This geode cake tutorial contains a recipe for a 3-layer, 8-inch chocolate cake with vanilla cream cheese frosting. It also includes step-by-step photos showing you how to decorate the outside of the cake to look like a geode rock formation.

What is a geode cake?

Geode cakes are meant to mimic the natural rock formation, with the baker typically carving out chunks from the cake and filling the cut-outs with “edible crystals” made out of rock candy or isomalt shards. The crystals are then painted multiple colors to emulate the look of real geodes themselves.

Pros and Cons of A Geode Wedding Cake

Geode cakes are a bit of an internet phenomenon on both Instagram and Pinterest (seriously, look up #geodecake); it was easy to feel inspired by photos of epic centerpieces that towered way over my head, with veins of edible gold running through the cake (like this one!).

After scrolling through all those photos, all I wanted to do was try making one myself! I had this crazy idea to make a geode cake that looked like the non-traditional engagement ring I chose—a cornflower blue sapphire haloed by diamonds on a platinum band. I was so excited that I forgot about two very important issues with geode cakes:

A lot of geode cakes look like vaginas.

There, I said it. Let’s get that elephant out the room early, lol. Granted, there are some cakes that worst offenders than others—pink geode cakes are notorious for looking like vaginas (there’s actually a famous bakery that sells pink ones they call “vageode cakes”… yikes!). I also think that ones that are painted ombre (where the center of the geode cutout is a darker color that gradates to a lighter version of that same color) look vaginal, too. I don’t know if I just have a dirty mind, but according to the response to my Instagram Stories, I don’t think I’m alone in my opinion. In any case, it’s weird that something so phallic (er… what’s the opposite of phallic? vaginal?) became the edible centerpiece in what’s often dubbed as “the most important day in a woman’s life”. But maybe that’s on purpose, lol.

Geode cakes are actually terrible to eat.

I don’t know if anybody saw my Instagram Stories last week, in which I made my very first geode cake ever (this one!) and taste-tested it, too. But spoiler alert: it turns out all those large chunks of rock crystals ruin the texture of a very soft, pillowy cake covered in even silkier buttercream. Plus, you could potentially chip your teeth on one of the sugar chunks!!! Many of you guys DM’ed me that, similar to most fondant wedding cakes, you’re not actually supposed to eat the crystals. That is, most people peel off/pick off/eat around the fondant parts of a wedding cake—you’re supposed to do the same with the crystals and not sit there and eat the entire thing like I was doing. Oops.

While this makes sense to me on a theoretical level, it also low key offends me. I want all parts of my wedding cake to be tasty—I don’t want to be picking around the gross/inedible parts of a colorful cake while wearing a very expensive white dress! Besides, there are so many good cake recipes (and designs!) out there that don’t require you to even do this kind of work to eat it. I quickly came to the consensus that a geode cake is NOT what I’m going to be making and serving at our wedding. Womp.

That being said, I still think that making a geode cake at home is a fun and creative way to spend your time. Besides—these cakes usually cost an arm and a leg to have custom made, and it turns out they’re actually quite easy to make at home! Here’s how:

Ingredients To Make A Geode Cake

Here are the key ingredients to make a geode cake design:

A Really Good Cake Recipe For The Base of Your Geode Cake

This should go without saying, but a good cake design should start off with a good cake recipe. One that’s tasty and comes together quickly because you’re going to be spending so much time on assembling the cake itself. For our cake today, I went with the chocolate cake recipe in my cookbook, Weeknight Baking. It’s ALMOST one bowl (technically you need two bowls: one for the dry ingredients, the other for the wet ones), and you don’t even need to pull out your stand mixer—you can just mix everything by hand!

A Really Good Frosting Recipe To Cover and Decorate Your Geode Cake

Good frosting recipes are silky and easy to smooth, but will hold its shape when applied to the cake. For this reason, most decorators choose a meringue-based buttercream like Swiss meringue or Italian meringue buttercream frosting. But these buttercream frostings are time-consuming to make, and between you and me, I like the taste of classic American buttercream—which is made with just confectioners’ sugar, butter, and vanilla—much better.

The key is to find a good buttercream frosting that “crusts” and hardens slightly when applied. For this cake, we’re going with a classic birthday cake type frosting from this awesome recipe in the Hummingbird High archive. Unlike most traditional American buttercream frostings, this recipe also has cream cheese (making it more of a cream cheese frosting tbh), giving it a wonderful tang that pairs well with the chocolate cake.

Rock Candy For Decorating Your Geode Cake

Remember those rock candy lollipops you could buy at science museums and boardwalk shops? You’re basically going to be buying that for this cake, but with the candy in chunks in a bag instead of wrapped around a lollipop stick.

I was an idiot and paid a premium for a bag off Amazon. I’d completely forgotten that rock sugar—which are basically bigger granules of rock candy, and unflavored to boot—is available for purchase at most Asian supermarkets at a third of the price. But be warned: rock sugar comes in MUCH bigger granules than the candy. It’s harder to eat (but maybe that doesn’t matter, since you’re not going to be eating it anyway per my rambling above?), but easier to work with when making your cake.

Food Coloring For Painting Your Rock Candy

You’ll need food coloring to paint the rock candy colors to mimic a geode. I used two different types of blues from this Americolor food coloring kit. In a pinch, you can get away with using just one color—you’ll still need to make two batches of food coloring for the full effect, but dye one with a higher quantity of the same food coloring to get it a darker shade than the other.

Alternatively, if you’re feeling lazy and/or don’t want to deal with buying a paintbrush (see next section), you can just buy different shades of rock candy on Amazon (in addition to the clear rock candy I got fleeced on, I briefly considered buying this dark blue shade and this light blue one of rock candy).

Vodka For Painting Your Rock Candy

If you’re using a food coloring gel like I am, you’ll need to thin the gel out with some vodka. The vodka also helps apply and adhere the color onto the rock candy without dissolving it completely like water would.

Edible Gold Or Silver Leaf For Decorating Your Rock Candy And Cake

Most geode cakes usually incorporate some sort of metallic, glittery patterning (see this cake as an example) to really bring life to the rock formation design. The best way to do this is with edible gold leaf, which is easily purchasable through Amazon.

For this cake, I used edible silver leaf I bought on my last trip to Japan—I thought that silver leaf was a rarity in the US, but it turns out you can also purchase it quite easily on Amazon. Good thing I lugged it back all that way, ha.

Baking Equipment and Tools To Make A Geode Cake

You need a handful of tools to make a geode cake:

A Rotating Cake Stand

Most geode cakes start with a perfectly smooth frosted cake. The best way to frost a perfectly smooth cake is with a rotating cake stand. I use a heavy-duty metal one that I got from a restaurant supply store; it’s very similar to this one by Ateco.

Metal rotating cake stands are great because they won’t move at all even if you accidentally knock it with your elbow (which I’ve done many times). But in a pinch, you can also use lighter weight plastic ones—I like this one by Wilton, which allows you to tilt the cake side by side to help with decorating.

Offset Spatulas

You’ll need a large offset spatula to smooth the cake’s sides, and a smaller one to cover the cake’s cut-outs with frosting. I know I sound like an ad for Amazon, but they actually sell reasonably priced sets of different sized offset spatulas that are perfect for this recipe.

A Serrated Knife

A sharp serrated knife is the best way to slice out the cut-outs for geode cake’s rock candy crevices. Try to get a smaller/shorter one, like this 5-inch one by Wusthof—the shorter length will make it easier to carve your cut-outs more accurately. In a pinch, a sharp paring knife will do, but a serrated knife will work better against the chilled cake crumb (more on that in a second).

A Small Paintbrush

If you didn’t buy colored rock candy, you’ll need a small paintbrush to paint food coloring onto your rock candy. I actually didn’t have a paintbrush on hand (I tried to buy one specifically for this project, but after biking to Fred Meyer’s in the pouring rain, I discovered I left my wallet at home and let out a roar of frustration so loud that the person in line behind me jumped lol), so I used a brush meant for brushing egg wash onto pies.

Because it’s much larger than the kind of paintbrush I wanted (which was something like these brushes), my coloring is more all over the place and less of the ombre coloring that’s traditional in geode cakes. But I actually ended up liking it more since it looked a lot less vaginal, so there’s that.

Tweezers

Finally, you’ll need some tweezers to apply the edible gold (or silver) leaf onto the cake.

How To Make A Geode Cake

Once you’ve frosted a perfectly smooth cake, it’s time to make your geode cake design!

1. Use a small serrated knife to carve out cut-outs in the cake.

Don’t worry too much about the shape and size of the cut-outs—just do what feels easiest! I literally just sliced out a chunk without thinking too much about it. You can do one giant cutout (which is traditional for geode wedding cakes), or do multiple ones like I did to make it look less vagina-y.

2. Use a small offset spatula to cover the cut-outs with frosting:

After you make your frosting, be sure to set aside at least ¼ cup to ⅓ cup of the frosting to use for this purpose. Unlike the rest of the cake, you don’t need to perfectly smooth the frosting on the cut-outs—after all, you’ll be covering it with rock candy! Also, don’t worry if any cake crumbs get into the frosting in the cut-outs. Again, you’re going to be covering that area anyway.

3. Use tweezers or your fingers to cover the cut-outs with rock candy:

The rock candy will be held in place with the frosting. You want to press firm enough so that the rock candy holds its place, but not so hard that you end up denting or destroying the cake inside. You’ll also want to cover any crumbs or exposed parts of cake with rock candy to hide them.

4. Use a paint brush to paint the centers of the rock candy-covered cut-outs with a darker color, then paint the cut-outs’ outer edges with a lighter color:

To make your “paint”, mix as many drops of food coloring as necessary to achieve the color of your choice with 1 teaspoon of vodka.

5. Tweeze gold or silver leaf onto the cake to finish the design:

Bakers making traditional geode wedding cake designs typically create a gold leaf border around the cut-outs. Again, I avoiding doing so because I thought this enhanced the vagina effect of the design, lol. So instead, I just placed silver leaf at random throughout the cake. But you do you!

Make It Weeknight Baking

Although I broke this down fairly easily, it can be time-consuming to make a geode cake—in fact, it took me almost the entire afternoon just to assemble, frost, and make the geode design. It would have taken all day if I’d made the cake in the same day, too.

Because I don’t like to spend eight consecutive hours in the kitchen all at once, I divided the recipe over a few days. I actually do this for many of the cake recipes in my cookbook, Weeknight Baking. Here’s how it went down:

1. 1. Day One: Make the Cake! (around 1 hour, including Bake Time)
      Follow the instructions in the recipe below to cool the cakes to room temperature, then turn each layer out into its own individual sheet of plastic wrap. Cover tightly with the plastic wrap and freeze overnight—do NOT refrigerate! Refrigerating cakes dries them out, while freezing the cakes locks the moisture in. In a pinch, I’d rather you leave the cakes wrapped at room temperature. However, I don’t recommend doing so; the cake has such a soft crumb that it’s much easier to carve when it has frozen overnight. So freeze the cakes!

1. 1. Day Two: Make the Frosting and Frost the Cake (around 1 to 1 ½ hours)
      In general, it will take about 10 minutes to make the frosting and then the rest of the time to assemble the layer cake and frost it perfectly smooth. Depending on your experience with frosting cakes, it could take far less (or far more!) time to do so—I’m a bit of a perfectionist, so it always takes me at least an hour to smoothen out my cake. Don’t forget to save at least ¼ cup to ⅓ cup of the frosting for your cut-outs the next day; you can place this frosting in an airtight container and refrigerate overnight.

1. Day Three: Make the Geode Cake Design (around 1 ½ hours) and Serve! 
   Follow the instructions above to complete your geode cake. You may want to warm your frosting before using on the cake—simply scoop it into a heatproof bowl and microwave it on low in 10 to 20 second bursts until creamy, using a rubber spatula to mix it up.

Best Geode Cake Tutorial Tips

• • {Ingredient Tip} I’m not usually one to harp on sifting ingredients (see: this article in Bon Appetit, where I talk about why you don’t really ever need to sift your flour), but for the frosting recipe, it’s especially important that you sift your confectioners’ sugar. The recipe uses a LOT of it, and you don’t want any lumps showing (especially when you’re trying to perfectly smooth a cake!).

• • {Cake Making Tip} For this cake recipe, it’s especially important to add the coffee while it’s still hot (almost boiling, if possible!). The hot coffee will bloom the cocoa powder in the recipe, giving it a deeper flavor and an extra-dark color that’s signature to this cake.

• • {Cake Making Tip} For even cake layers, I like to actually weigh out the layers with a digital scale to make sure they’re even. The easiest way to do this is to set a prepared cake pan on a digital scale and tare it to “0”. Pour batter into the pan until the scale registers the weight listed in the recipe (because yes, I’ve included the approximate weight of the batter needed for each pan!). Repeat with the second and third cake pan.

• • {Decorating Tip} In general, chilled cake is easier to carve; even if you don’t follow the weeknight baking schedule above (I get it, three days is a long time to wait for a cake!), I recommend baking the cakes the day before and freezing them overnight. Before making the frosting, set the cakes out on the counter and let them thaw slightly while making the frosting. Assemble and frost the cake as instructed above—at this point, the cake will be the perfect temperature (not rock hard, but still pretty chilled) for carving the cut-outs.

• {Decorating Tip} When filling your cut-outs the rock candy, start by placing the candy on the outside of the cut-outs and work your way in. The outer rock candy will help protect your hands from the frosting (though you’ll definitely still need to wipe them off as you go—this is a messy job!).