Heat oven to 375ºF.
Line bottom of 15x10x1-inch baking pan with parchment paper, set aside.
Arrange clean thin cotton towel (about 34x20 inches) onto counter.
Sprinkle generously with unsweetened cocoa, set aside.
Combine flour, ¼ cup cocoa, baking powder and salt in bowl, set aside.
Combine sugar, eggs and vanilla in another bowl, beat at high speed 5 minutes or until fluffy, thick and pale yellow color.
Stir melted butter into egg mixture, gently stir flour mixture into egg mixture until just combined.
Spread into prepared pan.
Bake 10-12 minutes or until center springs back when touched.
Run knife around edges to loosen sides.
Turn cake out onto prepared towel, remove parchment paper.
Roll up cake in towel, set aside to cool.
Using a mixer, eat ½ cup chilled whipping cream and ¼ cup powdered sugar at medium-high speed, scraping bowl often, until stiff peaks form.
Shape marzipan into mushrooms as best you can :) (if using)
Keep in the fridge until ready to decorate cake.
Place chocolate ganache (or chocolate hazelnut spread) and cream cheese in another bowl, beat at medium speed until well mixed.
Gently stir whipped cream mixture into chocolate mixture until just combined.
Cover, refrigerate at least one hour.
Combine chopped chocolate and whipping cream in bowl and set it over a pot of simmering water to melt.
Add butter at the end and set aside to cool slightly.
Unroll cake, spread small with chilled filling evenly
Reroll, refrigerate until ready to assemble.
Slice a third of the cake roll at an angle. Set aside
Put larger cake log first on a serving plate then attach the smaller piece so it angles out like a branch, secure with toothpicks or wooden skewers, as needed.
Carefully frost sides of cake.
Draw lines in frosting, using fork or tip of dinner knife to make it look like a tree bark
Sprinkle powdered sugar all over the cake
Garnish as you like with marzipan mushroom, or some rosemary sprigs or pine cones
Enjoy. Happy Holidays!