Yule log

1.    Preheat oven to 180C
2.    Prepare the pan: butter a 12×17-inch baking pan, line it with parchment paper and lightly grease the parchment too. 
3.    Mix dry ingredients: In a bowl, whisk together flour, cocoa powder, baking powder, and salt. Set aside.
4.    Whip egg whites: In a clean bowl, beat egg whites with 100g sugar on high speed for a couple of minutes, until stiff peaks form. Transfer to another bowl.
5.    Beat yolks: In the same mixing bowl, beat egg yolks, remaining sugar, oil, and vanilla on high speed for couple minutes, until thick and pale
6.    Combine mixtures:- Gently beat half of the whipped egg whites into the yolk mixture on low speed for 10 seconds. Add the remaining egg whites and beat again on low for 10 seconds.
7.    Add dry ingredients: fold in half of the flour gently with a spatula. Add the rest of the flour mixture and fold just until combined.
8.    Bake the cake: Spread the batter evenly in the prepared pan. Tap the pan gently on the counter to remove air bubbles. Bake for 15 minutes, until the cake springs back when lightly touched.
9.    Prepare to roll:
-    While the cake bakes, lay a large piece of parchment paper or a clean kitchen towel on the counter. (A towel helps prevent cracks.)
-    Dust it with about 3 tbsp (15g) cocoa powder using a fine mesh sieve.
10.    Roll the cake: once baked, invert cake immediately onto the cocoa-dusted parchment. Peel off the baking parchment from the bottom. Starting at the short end, roll up the warm cake gently but tightly inside the parchment. Let it cool completely.
11.    Make the whipped cream: In a large bowl, beat double cream, icing sugar, and cocoa powder on medium-high speed for a couple of minutes, until stiff peaks form.
12.    Fill the cake: Unroll the cooled cake gently spread the whipped cream evenly over the top, leaving about a ½-inch border around the edge. 
13.    Re-roll the cake: Carefully roll the cake back up (without the parchment). Transfer to a cutting board, wrap in plastic and refrigerate for at least 30 minutes before adding ganache.
14.    Make the ganache: Place chopped chocolate in a medium bowl. Heat cream in a saucepan until it just starts to simmer. Pour hot cream over the chocolate and let sit for a few minutes. Stir slowly until smooth and fully melted. The ganache will be thin - refrigerate uncovered for 30 minutes until it thickens.
15.    Assemble the log: Remove the rolled cake from the fridge. Place the cake on a serving platter. Spread thickened ganache evenly over the top and sides. Use a fork to create a bark-like texture in the ganache.