Prepare the Sponge Cake
Preheat oven to 350°F (175°C). Line a 10×15-inch jelly roll pan with parchment paper and lightly grease it.
Sift together flour, cocoa powder, baking powder, and salt. Set aside.
In a bowl, beat egg yolks with ¼ cup sugar until thick and pale. Stir in vanilla extract.
In another bowl, beat egg whites until soft peaks form. Gradually add the remaining ¼ cup sugar and beat until stiff peaks form.
Gently fold the yolk mixture into the whites. Sift in dry ingredients and fold gently.
Spread batter evenly in the pan and bake for 10–12 minutes, until the cake springs back when touched.
Roll the Cake
Turn the cake onto a clean kitchen towel dusted with powdered sugar. Remove parchment paper.
Starting at a short end, roll the cake with the towel. Cool completely.
Make the Whipped Cream Filling
Beat heavy whipping cream, powdered sugar, and vanilla extract until stiff peaks form.
Assemble the Cake
Unroll the cooled cake and spread whipped cream evenly. Re-roll the cake without the towel and place it seam-side down on a serving platter.
Prepare the Ganache
Heat heavy cream until it begins to simmer. Pour over chopped chocolate and let sit for 1 minute. Stir until smooth and glossy. Cool slightly to thicken.
Decorate the Cake
Spread ganache over the cake. Use a fork or spatula to create bark-like textures.
Dust with powdered sugar and add decorations like berries or meringue mushrooms.
