- For the sponge cake
- 25 grams Milk chocolate couveture
- 3 medium Eggs
- 2 tablespoons hot Water
- 50 grams Sugar
- 1 packet Vanilla sugar
- 50 grams Pastry flour
- 15 grams Cornstarch
- 1 generous pinch Baking powder
- For the chocolate buttercream
- Vanilla pudding powder
- 1 tablespoon Sugar
- 250 milliliters Milk
- 25 grams semisweet chocolate and Milk chocolate couveture
- 125 grams softened Butter
- 1 tablespoon rum
For the sponge cake: Chop the chocolate, place in a small bowl and melt over a hot water bath. Separate the eggs. Whip the egg whites until stiff. Whisk the egg yolks until frothy with the water, sugar and vanilla sugar. Fold in the egg whites. Combine the flour, cornstarch and baking powder then sift over the batter and fold in. Set 2-3 tablespoons batter aside. Line a baking sheet with parchment paper and spread the light batter over top.
Mix the melted chocolate into the reserved batter, transfer to a piping bag fitted with a small plain tip and pipe over the batter in thin evenly spaced lines. Bake in a preheated oven at 200°C (approximately 400°F) for about 12 minutes.
Immediately invert the cake onto a piece of parchment paper sprinkled with sugar, discard the used parchment paper and cover the sponge cake with a damp tea towel.
For the chocolate buttercream: Whisk the pudding powder, sugar and 4 tablespoons milk together. Bring the remaining milk to a boil, add the chocolate and pudding mixture, reduce the heat and stir until thickened. Remove from the heat, pour into a bowl then place over an ice bath to cool, stirring occasionally.
Beat the butter until smooth then gradually beat in the pudding. Spread over the sponge cake and cut into 12 (9 x 9 cm) (approximately 4 x 4 inch) rectangles. Carefully roll up each rectangle so that the corners touch.