For the Sponge Batter

• 6 eggs (separated)
• 1 pinch salt
• 1 packet vanilla sugar (approx. 10g or 1 tsp vanilla extract)
• 6 tbsp granulated sugar
• 6 tbsp all-purpose flour

For the Silky Chocolate Cream

• 100g dark chocolate (broken into small pieces)
• 2 tbsp cocoa powder
• 100g butter (room temperature)
• 100ml heavy whipping cream
• 100g powdered sugar

Step 1: Prepare the Sponge Batter

Separate the eggs. Whip the egg whites with a pinch of salt until stiff peaks form. Gradually add the vanilla sugar, then the granulated sugar tablespoon by tablespoon, whipping continuously. Gently fold in the egg yolks one by one, and finally, carefully fold in the flour using a wooden spoon or spatula to keep the batter light and airy.

Step 2: Bake the Sponge

Spread the batter evenly onto a baking sheet lined with parchment paper, making sure it is not spread too thick. Bake in a preheated oven at 160°C (320°F) for approximately 15-20 minutes until golden and springy to the touch.

Step 3: The Rolling Technique

Immediately after removing from the oven, flip the hot sponge onto a damp kitchen towel so the parchment paper is on top. Carefully peel off the paper, then tightly roll up the sponge together with the kitchen towel. Let it cool in this rolled shape, unrolling and rerolling it a few times during the cooling process to maintain flexibility and prevent cracking.

Step 4: Make the Silky Chocolate Cream

Melt the dark chocolate pieces over a double boiler. Remove from the heat, then add the cocoa powder, butter, and heavy cream. Use a hand mixer to beat the mixture until smooth. Sift in the powdered sugar and continue mixing until you achieve a glossy, soft, and spreadable cream.

Step 5: Assemble and Serve

Gently unroll the cooled sponge and spread the room-temperature chocolate cream evenly over the surface. Carefully roll it back up. Dust the top with powdered sugar before slicing and serving.