Preheat oven to 350°F (175°C). Line a 10x15-inch jelly roll pan with parchment paper, leaving an overhang on the sides.

In a large bowl, beat eggs and sugar with an electric mixer until pale and thick, about 5 minutes. Mix in vanilla extract.

Sift together flour, cocoa powder, and salt. Gently fold into the egg mixture until just combined.

Pour batter into prepared pan, spreading evenly. Bake for 12-15 minutes until the cake springs back when touched.

While warm, dust the cake with powdered sugar. Place a clean kitchen towel over it, then carefully flip onto a flat surface. Peel off parchment paper.

Starting from the short end, roll the cake up with the towel inside. Let cool completely on a wire rack.

For the ganache: Heat cream until simmering, then pour over chopped chocolate. Let sit for 2 minutes, then stir until smooth. Cool slightly.

Unroll the cake, spread half the ganache evenly, then re-roll without the towel. Transfer to a serving platter.

Frost the outside with remaining ganache. Use a fork to create bark-like texture. Decorate with powdered sugar, berries, and meringue mushrooms.