Geode Cake

A meeting of nature and confectionery: this cake looks as if we've hidden a precious mineral, a geode, inside. The sparkling crystals are actually made of sugar, and the cavity of the cake is carved out with a knife. This is the high school of edible sculpture, but the technique can be mastered at home. The base is a massive, buttery sponge that withstands shaping.
🕒 Prep Time 1 hr
🍳 Cook Time 30 mins
Total Time 1 hr 30 mins
🍽️ Servings 10 servings
🔥 Calories 680 kcal
🌍 Cuisine International, Modern Patisserie

Ingredients

Equipment Needed

  • 2 x 20 cm cake tins
  • Electric whisk
  • Palette knife
  • Sharp paring knife (for carving)
  • Fine brush (for painting)

Allergen Information

⚠️ Cereals containing gluten
⚠️ Eggs
⚠️ Milk

Instructions

1

Preheat the oven to 180°C. Grease and flour the tins. Sift together the flour, salt, and baking powder.

Tip: Sifting aerates the flour and distributes the baking powder so there are no large holes in the cake.
2

Cream the butter with the sugar until pale, then add the eggs one by one.

Tip: The eggs and butter should be the same temperature, otherwise the fat will separate (curdle) and the cake won't rise nicely.
3

Alternately fold in the flour mixture and the milk. Do not overmix!

Tip: Gluten formation starts upon contact with flour. If you overmix, the cake will be chewy, not crumbly.
4

Bake for 25-30 minutes (skewer test). Cool on a wire rack.

Tip: The wire rack allows air to circulate underneath, preventing a soggy bottom.
5

Make the cream: whip the double cream, mix the mascarpone with the icing sugar, then fold together.

Tip: The fat droplets in the cream trap the air (foam). If you overbeat, the fat separates and becomes butter.
6

Fill the cake and coat the outside. Chill.

Tip: The shape holds better during carving if the cream is cold.
7

Cut a V-shaped hollow into the side. Coat the cut with cream and stick in the rock candy.

Tip: Use smaller and larger pieces for a natural effect.
8

Paint the crystals with dye diluted with alcohol: darker inside, lighter outwards. Paint the rim gold.

Tip: Alcohol evaporates quickly and doesn't dissolve the sugar like water would.

Recipe FAQ

Why cream the butter and sugar?
To incorporate air into the batter (creaming method). The sharp edges of the granulated sugar cut tiny bubbles into the butter, making the cake light.
Can I use plain sugar for the decoration?
The larger crystals of rock candy replicate the natural, irregular beauty and light refraction of minerals better.

Ingredients

  • 300 g Plain flour
  • 250 g Caster sugar (fine grain)
  • 200 g Butter (room temperature)
  • 4 pcs Eggs (large)
  • 200 ml Whole milk (3.5%)
  • 12 g Baking powder
  • 2 g Salt
  • 400 g Mascarpone or cream cheese
  • 150 g Icing sugar
  • 200 ml Double cream (cold)
  • 1 tsp Vanilla extract
  • 150 g Rock candy (clear/white)
  • 1 set Gel food colouring (blue, turquoise, gold)
  • 1 capful Vodka or clear spirit (for painting)