Step 1: Prepare the Sponge Cake

1. Preheat your oven to 350°F (175°C). Line a 10×15-inch jelly roll pan with parchment paper, and lightly grease the paper to prevent the cake from sticking.
2. In a large mixing bowl, beat the egg yolks with half of the sugar (1/4 cup) until pale and thick, about 2-3 minutes. Add the vanilla extract and mix to combine.
3. In a separate bowl, sift together the flour, cocoa powder, and salt. Set aside.
4. In another clean mixing bowl, beat the egg whites on medium speed until soft peaks form. Gradually add the remaining 1/4 cup of sugar and continue beating until stiff peaks form.
5. Gently fold the egg whites into the egg yolk mixture, being careful not to deflate the batter. Fold in the sifted dry ingredients gradually, mixing just until combined.
6. Spread the batter evenly into the prepared pan, smoothing the top with a spatula.
7. Bake for 10-12 minutes, or until the cake springs back when lightly touched. Avoid overbaking, as this will make it difficult to roll without cracking.

Step 2: Roll the Cake

1. While the cake is still warm, carefully lift it out of the pan using the parchment paper. Place it on a clean, flat surface.
2. Dust a clean kitchen towel with powdered sugar and place it over the top of the cake. Carefully roll the cake and towel together, starting from the short end. This initial roll helps shape the cake so it won’t crack when filled.
3. Let the cake cool completely while rolled up, about 20-30 minutes.

Step 3: Make the Cream Filling

1. In a large mixing bowl, beat the chilled heavy cream with powdered sugar and vanilla extract until soft peaks form. For additional flavor, you can add instant espresso powder or cocoa powder to the whipped cream.
2. Unroll the cooled cake carefully and spread the cream filling evenly over the surface, leaving a 1/2-inch border around the edges.
3. Gently roll the cake back up (without the towel), keeping it tight but not pressing too hard, so the filling stays in place.

Step 4: Prepare the Chocolate Ganache Frosting

1. Place the chopped chocolate in a heatproof bowl.
2. In a small saucepan, heat the heavy cream until it just begins to simmer, then pour it over the chocolate. Let it sit for a minute, then add the butter and whisk until smooth and glossy.
3. Let the ganache cool for 10-15 minutes, or until it thickens to a spreadable consistency.

Step 5: Frost the Yule Log Cake

1. Trim the ends of the rolled cake to create clean edges. If you’d like, cut a small piece from one end at an angle and place it on the side to resemble a branch.
2. Spread the chocolate ganache evenly over the entire surface of the cake, including the “branch” if you added one.
3. Use a fork or spatula to create a bark-like texture on the ganache, dragging the fork along the surface in wavy lines to mimic wood grain.

Step 6: Decorate the Yule Log

1. Dust the cake with powdered sugar to create a snowy effect.
2. Garnish with fresh rosemary sprigs or mint leaves to resemble greenery, and add a few cranberries or red berries for a festive touch.
3. For a traditional Yule log look, add meringue mushrooms around the log or on top.
4. Chill the cake in the refrigerator for at least 30 minutes to allow the ganache to set before serving.