Step 1: Preparing the Sponge Cake

1. Preheat the Oven: Begin by preheating your oven to 350°F (175°C). Line a jelly roll pan with parchment paper.
2. Whip the Eggs and Sugar: In a large mixing bowl, beat the eggs and sugar together until pale and fluffy. This step is key for creating a light and airy sponge.
3. Add Dry Ingredients: Sift together flour and cocoa powder. Gently fold the dry ingredients into the egg mixture, being careful not to deflate the batter.
4. Spread and Bake: Spread the batter evenly on the prepared pan and bake for 10–12 minutes. The cake should be springy to the touch when it’s done.

Step 2: Rolling the Sponge Cake

1. Cool and Roll: Place a clean towel dusted with powdered sugar on a flat surface. Once the cake has slightly cooled, transfer it to the towel, then roll it gently while warm.
2. Let It Cool Completely: Allow the cake to cool in its rolled shape, which prevents cracking when you later add the filling.

Step 3: Making the Filling and Ganache

1. Prepare Whipped Cream Filling: Whip heavy cream with a bit of sugar until stiff peaks form. This light, fluffy filling adds creaminess to each bite.
2. Make the Chocolate Ganache: Heat the remaining heavy cream and pour it over the chopped chocolate. Stir until smooth, then add butter for a rich, silky texture.

Step 4: Assembling the Yule Log

1. Unroll and Spread Filling: Carefully unroll the cooled sponge and spread the whipped cream filling evenly across the cake.
2. Roll Again and Chill: Roll the cake back up (without the towel this time) and refrigerate to set the filling.

Step 5: Decorating the Yule Log

1. Apply Ganache: Spread the chocolate ganache over the rolled cake, using a spatula to create a bark-like texture.
2. Add Decorative Touches: For a festive touch, dust with powdered sugar for a snowy effect, or add garnishes like meringue mushrooms, fresh berries, or sprigs of rosemary.