Combine the chopped white chocolate and heavy cream in a small saucepan over medium heat. Stir continuously until the chocolate melts completely. Remove from heat and stir in peppermint extract if using. Chill in the refrigerator for at least 4 hours to set.

Preheat the oven to 375°F (191°C). Line and lightly grease an 18×13 inch baking sheet with parchment paper. Microwave 60 ml vegetable oil for 1 minute until very hot. Whisk in sifted cocoa powder until dissolved. Add espresso/coffee powder and sea salt, stirring well. Pour in whole milk and vanilla extract and let cool slightly. Add all 6 egg yolks and mix thoroughly. Sift in the cake flour and gently combine with a spatula until smooth.

In a clean stand mixer bowl, whip the egg whites on medium speed until foamy. Add cream of tartar, then gradually add granulated sugar while increasing speed to high. Whip until soft peaks form.

Fold one-third of the whipped egg whites into the egg yolk and flour mixture carefully to lighten the batter. Gently fold in the remaining egg whites in two additions.

Pour the batter into the prepared baking sheet and smooth the surface. Bake at 375°F (191°C) for 15-16 minutes. Allow to cool for 15 minutes.

Transfer the chilled white chocolate mixture to a stand mixer bowl and whip until lightened.

Flip the cake onto a large piece of parchment paper, skin side down. Spread the white chocolate peppermint filling evenly over the cake. Carefully roll the cake with the parchment paper, finishing with the seam side down. Seal the ends of the parchment paper and refrigerate to chill.

Place chopped dark chocolate in a medium heat-safe bowl. Heat heavy cream in a small saucepan to a simmer and pour over the chocolate. Let it sit for 5 minutes, then whisk until slightly thickened.

Remove the rolled cake from the fridge and trim both ends. Cut a 3-inch length from one side at a 45-degree angle to create branches. Secure branches with toothpicks on a cake board using some ganache to hold the cake steady. Spread the chocolate ganache all over the cake surface with a spatula. Use a fork to draw bark-like lines on the ganache. Attach almond pine cones, meringue mushrooms, sugared cranberries, and rosemary using remaining ganache as glue. Cover loosely with plastic wrap and chill in the fridge to set the ganache.

Cut into slices with a sharp serrated knife and serve chilled or at room temperature.