Preheat Oven: Preheat your oven to 350°F (175°C). Line a 10×15-inch baking sheet with parchment paper and lightly grease the paper.

Prepare the Batter: In a large bowl, beat the egg yolks with 1/3 cup of sugar until thick and pale. In a separate bowl, whisk together the flour, cocoa, baking powder, and salt. Gradually add the dry ingredients to the egg yolk mixture, mixing until smooth.

Whip Egg Whites: In a clean bowl, beat the egg whites until soft peaks form. Gradually add the remaining 1/3 cup sugar, continuing to beat until stiff peaks form.

Combine: Gently fold the egg whites into the batter, taking care not to deflate the mixture.

Bake: Pour the batter into the prepared baking sheet and spread it evenly. Bake for 12-15 minutes, or until the cake springs back when touched.

Cool and Roll: Once baked, remove the cake from the oven and allow it to cool for about 5 minutes. Dust a clean kitchen towel with powdered sugar. Invert the cake onto the towel and peel off the parchment paper. While still warm, roll the cake up with the towel and set aside to cool completely.

Prepare the Filling: While the cake cools, whip the heavy cream with powdered sugar and vanilla extract until stiff peaks form.

Prepare the Ganache: In a small saucepan, heat the heavy cream over low heat until it begins to steam. Pour over the chopped chocolate and let sit for 2-3 minutes. Stir until smooth and glossy.

Assemble the Log: Unroll the cooled cake and spread an even layer of whipped cream filling over the entire surface. Carefully roll the cake back up without the towel.

Decorate: Place the rolled cake seam-side down on a platter. Spread the chocolate ganache over the top and sides. Use a fork to create a bark-like texture. Optionally, decorate with powdered sugar or fresh berries.

Chill: Refrigerate for at least 1 hour before serving to allow the cake to set.