Preheat your oven to 180°C (350°F) and prepare a 10x15 inch jelly roll pan with parchment paper.

Whisk eggs and granulated sugar until pale and fluffy, about 5-7 minutes. Sift flour, cocoa powder, baking powder, and salt together, then fold into the egg mixture with melted butter.

Pour batter into the prepared pan and bake for 12-15 minutes until the cake springs back when pressed.

Dust a clean kitchen towel with powdered sugar. Once the cake is done, cool for a minute, flip onto the towel, and roll it up with the towel inside.

For ganache, heat heavy cream until simmering, pour over chopped chocolate, let sit for 2-3 minutes, then stir in butter until smooth.

Beat softened butter until creamy, gradually add powdered sugar and cocoa powder, then mix in heavy cream and vanilla until fluffy.

Unroll the cooled sponge cake, spread chocolate ganache, and roll it back up without the towel, seam-side down on a platter.

Cover the log with buttercream frosting, creating a textured surface resembling tree bark.

Dust with icing sugar and decorate with fresh berries or mint leaves if desired.

Refrigerate for at least 1 hour before serving, then slice and enjoy.