Cake Preparation: Begin by preparing a chocolate sponge cake batter by whisking together eggs, sugar, and vanilla extract until light and fluffy.
Adding Dry Ingredients: Sift together cocoa powder, flour, baking powder, and salt. Gradually fold the dry ingredients into the egg mixture until well combined.
Baking Process: Spread the batter evenly onto a parchment-lined baking sheet and bake in a preheated oven until the cake is set and springs back when lightly touched.
Filling Preparation: Meanwhile, prepare the chocolate truffle filling by heating heavy cream until simmering, then pouring it over chopped chocolate.
Assembly: Once the cake is baked and cooled slightly, spread the chocolate truffle filling evenly over the surface.
Chilling and Serving: Wrap the rolled cake in plastic wrap and refrigerate for at least an hour to set the filling.