For key visual step-by-step photos, refer to the body of the post.

Make the white chocolate peppermint filling:

• Combine the chopped white chocolate and heavy cream into a small saucepan and bring it to medium heat.
• Stir until all the chocolate is melted.
• Remove from heat and transfer to a bowl. Stir in peppermint extract (if using).
• Chill the mixture in the fridge at least 4 hours.

Make the chocolate cake:

• Preheat oven to 375°F/191°C.
• Line and lightly grease an 18" by 13" baking sheet with parchment paper.
• Pour 60ml of vegetable oil into a heat-safe large bowl and microwave on high power for 1 minute, or until very hot.
• Add cocoa powder to the hot oil and stir to dissolve with a whisk or spatula.
• Next, add in espresso/coffee powder (if using), sea salt and give it a stir.
• Pour in milk and vanilla extract. Let the mixture cool down slightly.
• Next, add in egg yolks all at once into the chocolate mixture and mix well.
• Sift in the cake flour and combine with a spatula. Set aside.
• In a clean stand mixer bowl fitted with a whisk attachment, whip egg whites on medium speed until foamy, and add in cream of tartar.
• Gradually add in sugar and increase to high speed, whipping the meringue to soft peaks.
• Use a spatula to fold the whipped egg whites (in one-third additions) into the egg yolk + chocolate cake flour mixture, taking care not to deflate the batter.
• Pour the cake batter into the baking sheet, and smooth the surface with an offset spatula.
• Tap the pan a few times to release any trapped air bubbles.
• Bake at 375°F/191°C for 15-16 minutes, or until the top is dry and springy to the touch.
• Remove from oven and carefully bang the cake pan on the counter.
• Let the cake cool for 15 minutes.
• In the meantime, place the white chocolate mixture into a stand mixer fitted with a whisk attachment and whip until lightened, but not overwhipped.

Roll the cake:

• Flip the cake and transfer to a large piece of parchment paper, skin side down.
• Use an offset spatula to spread the white chocolate filling over the surface of the entire cake.
• Starting lengthwise, carefully roll the cake up with the parchment paper, ending with the seam side down.
• Seal ends of the parchment paper and place cake onto a tray and place into the fridge to chill.

Make the chocolate ganache (tree bark):

• Place dark chocolate in a medium heat-safe bowl.
• Add heavy cream to a small saucepan and heat to a simmer.
• Remove from heat, and pour the hot cream into the dark chocolate.
• Let the mixture sit for 5 mins.
• Whisk the chocolate ganache for 15-30 seconds, until slightly thickened, but don't overwhip.

Decorate:

• Remove rolled cake from the fridge.
• Trim both ends of the cake (enjoy as a snack!)
• Cut a 3" length from one side of the cake.
• From that 3" length, make another cut at a 45 degree angle, splitting it in half (to make the branches).
• Add a little chocolate ganache to the cake board/plate to help the cake from moving.
• Place the cake onto the cake board.
• Use toothpicks to secure the branches to the main cake. 
• Work quickly to spread the chocolate ganache frosting on the surface of the cake with a spatula or offset spatula; reserve some ganache for additional decorations.
• Use a fork to drag/draw lines over the cake to resemble an actual tree log bark.
• Use remaining ganache as "glue" to stick pine cones, meringue mushrooms and sugared cranberries and rosemary on the surface of the cake.
• Dust with matcha powder and powdered sugar to emulate moss and snow.
• Lightly cover yule log with plastic wrap and chill in the fridge, for the ganache/bark to set.
• To serve, cut cake slices with a sharp serrated knife.