Step 1: Prepare the Cake: Preheat oven to 350°F (175°C). Line a 10x15-inch jelly roll pan with parchment paper and lightly grease. In a large bowl, beat eggs and sugar on high speed until thick, pale, and fluffy (about 5 minutes). Gently fold in flour, cocoa powder, and salt until fully combined. Add vanilla extract. Pour batter evenly into the prepared pan and spread smoothly. Bake for 12–15 minutes or until the cake springs back when touched.

Step 2: Roll the Cake: While still warm, invert the cake onto a clean kitchen towel dusted with powdered sugar. Carefully peel off the parchment paper. Roll the cake gently with the towel from the short end. Allow it to cool completely while rolled.

Step 3: Prepare the Filling: In a chilled bowl, whip heavy cream with powdered sugar and vanilla until soft peaks form.

Step 4: Unroll and Fill the Cake: Gently unroll the cooled cake. Spread the whipped cream evenly over the surface, leaving a 1-inch border on one side. Carefully roll the cake back up without the towel. Place seam-side down on a serving platter.

Step 5: Make the Ganache: Heat cream in a small saucepan until just simmering. Pour over chopped chocolate in a heatproof bowl. Let sit 1–2 minutes, then stir until smooth. Stir in butter if using. Let ganache cool slightly to thicken but remain pourable.

Step 6: Frost and Decorate: Pour or spread ganache over the rolled cake, covering all sides. Use a fork or spatula to create bark-like texture. Decorate with powdered sugar, meringue mushrooms, berries, or mint leaves.