Step 1: Prepare the Sponge Cake

1. Preheat your oven to 375°F (190°C). Grease a 10×15-inch jelly roll pan and line it with parchment paper, ensuring the paper extends slightly over the edges for easy removal.
2. In a large mixing bowl, beat the eggs and granulated sugar together on high speed until pale, thick, and tripled in volume, about 5–7 minutes. Add the vanilla extract and mix to combine.
3. In a separate bowl, whisk together the flour, cocoa powder, baking powder, and salt. Gradually fold the dry ingredients into the egg mixture using a spatula, being careful not to deflate the batter.
4. Pour the batter into the prepared pan, spreading it evenly with an offset spatula. Bake for 10–12 minutes, or until the cake springs back when lightly pressed.

Step 2: Roll the Cake

1. While the cake is baking, lay a clean kitchen towel on a flat surface and dust it generously with powdered sugar.
2. Once the cake is out of the oven, carefully invert it onto the prepared towel. Remove the parchment paper and, starting at one short end, roll the cake and towel together into a spiral. Allow it to cool completely in this rolled shape.

Step 3: Prepare the Filling

1. In a mixing bowl, beat the heavy whipping cream, powdered sugar, and vanilla extract on medium-high speed until stiff peaks form.
2. For a richer filling, fold in cocoa powder or mascarpone cheese. Refrigerate until ready to use.

Step 4: Assemble the Cake

1. Gently unroll the cooled cake and spread the filling evenly across the surface, leaving a 1-inch border around the edges.
2. Carefully roll the cake back up without the towel, starting at the same short end. Place the rolled cake seam-side down on a serving platter or baking sheet.

Step 5: Frost the Cake

1. In a mixing bowl, beat the butter until creamy. Add the powdered sugar, cocoa powder, heavy cream, and vanilla extract, mixing until smooth and spreadable.
2. Using an offset spatula, spread the frosting over the rolled cake, covering it completely. Use a fork or spatula to create a bark-like texture.

Step 6: Decorate the Cake

1. Dust the cake with powdered sugar to resemble snow.
2. Add meringue mushrooms, sugared cranberries, and rosemary sprigs around the base for a woodland effect. Garnish with chocolate shavings or edible glitter for extra flair.
3. Chill the cake for at least 1 hour before serving to allow the flavors to meld.