Preheat the oven to 350°F (175°C)
Line a jelly roll pan with parchment paper
Grease the parchment lightly
Separate the eggs
Beat the egg yolks with sugar until pale
Add vanilla and cocoa powder
Whip the egg whites until stiff peaks form
Fold the egg whites into the yolk mixture
Spread the batter evenly in the prepared pan
Bake for 10 to 12 minutes
Lay a clean kitchen towel on a flat surface
Dust the towel with powdered sugar
Turn the cake out onto the towel
Peel off the parchment paper
Roll the cake up in the towel while warm
Let the cake cool completely
Make the filling with whipped cream or buttercream
Unroll the cooled cake
Spread the filling evenly over the cake
Roll the cake back up tightly
Trim the ends if needed
Make the frosting with chocolate buttercream or ganache
Cover the cake with frosting
Use a fork to create bark-like texture
Dust with powdered sugar
Decorate with meringue mushrooms, berries, or rosemary if desired
Chill before serving