Geode Cake

By
Kristina Vanni
Kristina Vanni
Kristina Vanni
An internationally recognized culinary authority, Kristina Vanni is well-known for her recipe development, food photography, and experience as a TV show host.
Learn about The Spruce Eats' Editorial Process
Updated on 11/25/21
Geode Cake

The Spruce/ Kristina Vanni

Prep: 45 mins
Cook: 30 mins
Cool Cakes: 2 hrs
Total: 3 hrs 15 mins
Servings: 12 servings
Yield: 1 cake

Geode cakes are stunningly decorated layer cakes meant to mimic the famous natural formation of rock and precious and semiprecious stones. Pieces of the finished and frosted cake are cut out, and then the cavity is filled with edible crystals made out of rock candy. Although it might seem like a lot of work, it actually isn't much more than making a layered and frosted cake, especially if you're buying the rock candy and not making it (you could, using isomalt). Use loose rock candy or the classic rock candy on a stick—just remove it from the stick before arranging it on the cake.

To make a realistic geode cake, decide on your favorite color palette for the geode. Start by selecting the main color of the stones—any hue will be beautiful. Purchase either a lighter shade of that same color or white rock candy to help create the ombré effect similar to that of real rock formations. Finally, purchase edible gold dust, gold shimmer sprinkles, or flakes to paint around the edges of the geode formation.

The amount of candy needed depends on how much you'd like to use on the cake and on how many cutouts you want it to have. The best course of action is to place enough candy to cover all the surfaces without crowding them. Rock candy crystals come in bags of one pound or more, so you'll get enough for this three-layer cake when you buy a one-pound bag each of colored and white candy. For easy decoration, we suggest you have at hand an offset spatula and food tweezers to easily frost the cake and place the rock candy in its place.

Ingredients

For the Cake:

  • 1 cup unsalted butter, softened

  • 2 cups sugar

  • 4 large eggs

  • 3 cups cake flour, sifted

  • 1 tablespoon baking powder

  • 1/2 teaspoon kosher salt

  • 1 cup milk

  • 1 1/2 teaspoons pure vanilla extract

For the Buttercream Frosting:

  • 2 (1-pound) boxes confectioners' sugar

  • 1 cup unsalted butter, softened

  • 6 to 8 tablespoons milk, divided

  • 2 teaspoons pure vanilla extract

For the Decoration:

  • Colored rock candy

  • White rock candy

  • Edible gold dust

Steps to Make It

Make the Cakes

  1. Gather the ingredients.

    Ingredients for making a geode cake

    The Spruce / Kristina Vanni

  2. Preheat oven to 350 F. Grease and flour 3 (8-inch-round) baking pans. Alternatively, if you only have 1 or 2 (8-inch-round) baking pans, each layer can be baked one at a time. In a large bowl, cream together butter and sugar until light and fluffy, either by hand or with the help of a standing mixer set with the paddle attachment.

    Butter and sugar in a mixing bowl

    The Spruce / Kristina Vanni

  3. Add eggs one at a time to creamed mixture, beating well after each addition.

    Adding eggs to the creamed butter and sugar

    The Spruce / Kristina Vanni

  4. In another large bowl, mix together cake flour, baking powder, and salt.

    Cake flour, baking powder, and salt in a bowl

    The Spruce / Kristina Vanni

  5. Add flour mixture to butter mixture, alternating with milk and vanilla extract. Mix well after each addition until you have a smooth batter. Do not overbeat.

    Getting ready to add flour mixture to butter mixture

    The Spruce/ Kristina Vanni

  6. Evenly divide batter into 3 prepared pans. Bake for 20 to 25 minutes or until a tester inserted into cake comes out clean.

    Geode cake batter in three 8-inch-round pans

    The Spruce / Kristina Vanni

  7. Cool in pans for 10 minutes. Remove cake layers from pans and cool completely on wire racks for 1 to 2 hours. The cakes need to be completely cold before frosting them.

    Three round cakes cooling on a wire rack

    The Spruce / Kristina Vanni

Make the Buttercream and Frost the Cake

  1. Gather the ingredients.

  2. To prepare buttercream frosting, combine confectioners' sugar, butter, 6 tablespoons of the milk, and vanilla extract in the large bowl of a standing mixer. Using the whip attachment, beat at medium speed for 1 to 2 minutes, until creamy. If necessary, add more of the remaining milk, half a tablespoon at a time, until frosting achieves desired consistency.

    Powdered sugar and butter for making the frosting

    The Spruce / Kristina Vanni

  3. Place first cake layer on a serving platter or cake stand. Top with some of the buttercream frosting. Place another layer on top and repeat above process. Place the third layer and cover in frosting.

    Topping a cake with buttercream frosting

    The Spruce / Kristina Vanni

  4. Using remaining frosting, evenly coat top and sides of 3-layer cake. Reserve a small amount of frosting to adhere rock candy pieces when decorating.

    Geode cake covered in buttercream frosting

    The Spruce / Kristina Vanni

Carve Out and Decorate the Cake

  1. Using a small, serrated knife, cut out the shape of your geode.

    A section of cake is removed for a crevasse

    The Spruce / Kristina Vanni

  2. Frost crevasse with remaining frosting and press colored rock candy into the deepest part of the crevasse and most of the way up the sides.

    Cake crevasse frosted and studded with purple rock candy

    The Spruce / Kristina Vanni

  3. Use white rock candy to surround colored rock candy.

    Purple rock candy is edged with white rock candy

    The Spruce / Kristina Vanni

  4. Use edible gold dust to paint the edges around the white rock candy. 

    Cake crevasse edged with edible gold dust

    The Spruce / Kristina Vanni

How to Store and Cut a Geode Cake

Once completed, a geode cake can be refrigerated for up to four days until ready to serve, just let the cake rest at room temperature for a whole hour before slicing. It is best to cut the geode cake from the undecorated side first, and once slices have been plated for your guests, place a few loose pieces of rock candy on the side for additional decoration.

Helpful Links

Nutrition Facts (per serving)
650 Calories
33g Fat
83g Carbs
6g Protein
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Nutrition Facts
Servings: 12
Amount per serving
Calories 650
% Daily Value*
Total Fat 33g 43%
Saturated Fat 20g 100%
Cholesterol 146mg 49%
Sodium 254mg 11%
Total Carbohydrate 83g 30%
Dietary Fiber 1g 2%
Total Sugars 56g
Protein 6g
Vitamin C 0mg 0%
Calcium 128mg 10%
Iron 3mg 17%
Potassium 114mg 2%
*The % Daily Value (DV) tells you how much a nutrient in a food serving contributes to a daily diet. 2,000 calories a day is used for general nutrition advice.
(Nutrition information is calculated using an ingredient database and should be considered an estimate.)