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

Make the white chocolate peppermint filling:

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

Make the chocolate cake:

1. Preheat oven to 375°F/191°C.
2. Line and lightly grease an 18" by 13" baking sheet with parchment paper.
3. Pour 60ml of vegetable oil into a heat-safe large bowl and microwave on high power for 1 minute, or until very hot.
4. Add cocoa powder to the hot oil and stir to dissolve with a whisk or spatula.
5. Next, add in espresso/coffee powder (if using), sea salt and give it a stir.
6. Pour in milk and vanilla extract. Let the mixture cool down slightly.
7. Next, add in egg yolks all at once into the chocolate mixture and mix well.
8. Sift in the cake flour and combine with a spatula. Set aside.
9. 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.
10. Gradually add in sugar and increase to high speed, whipping the meringue to soft peaks.
11. 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.
12. Pour the cake batter into the baking sheet, and smooth the surface with an offset spatula.
13. Tap the pan a few times to release any trapped air bubbles.
14. Bake at 375°F/191°C for 15-16 minutes, or until the top is dry and springy to the touch.
15. Remove from oven and carefully bang the cake pan on the counter.
16. Let the cake cool for 15 minutes.
17. 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:

1. Flip the cake and transfer to a large piece of parchment paper, skin side down.
2. Use an offset spatula to spread the white chocolate filling over the surface of the entire cake.
3. Starting lengthwise, carefully roll the cake up with the parchment paper, ending with the seam side down.
4. 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):

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

Decorate:

1. Remove rolled cake from the fridge.
2. Trim both ends of the cake (enjoy as a snack!)
3. Cut a 3" length from one side of the cake.
4. From that 3" length, make another cut at a 45 degree angle, splitting it in half (to make the branches).
5. Add a little chocolate ganache to the cake board/plate to help the cake from moving.
6. Place the cake onto the cake board.
7. Use toothpicks to secure the branches to the main cake. 
8. 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.
9. Use a fork to drag/draw lines over the cake to resemble an actual tree log bark.
10. Use remaining ganache as "glue" to stick pine cones, meringue mushrooms and sugared cranberries and rosemary on the surface of the cake.
11. Dust with matcha powder and powdered sugar to emulate moss and snow.
12. Lightly cover yule log with plastic wrap and chill in the fridge, for the ganache/bark to set.
13. To serve, cut cake slices with a sharp serrated knife.