Preheat and Prepare: Preheat oven to 350°F (175°C). Line a 10×15-inch jelly roll pan with parchment paper.

Make the Cake: In a bowl, beat egg yolks and 1/2 cup sugar until thick and pale. Stir in vanilla. In another bowl, whisk flour, cocoa powder, and salt. In a separate bowl, beat egg whites until soft peaks form. Gradually add remaining sugar and beat until stiff peaks form. Fold the yolk mixture into the egg whites gently. Sift the dry ingredients over and fold carefully.

Bake: Spread batter evenly in the prepared pan. Bake for 12-15 minutes. Immediately remove the cake. Place a clean towel on top, dust with powdered sugar, and roll the cake with the towel. Cool completely.

Prepare the Filling: Beat heavy cream, powdered sugar, and vanilla extract until stiff peaks form.

Prepare the Frosting: Heat cream until warm. Pour over chopped chocolate and let sit for a few minutes. Stir until smooth and let cool.

Assemble the Cake: Carefully unroll the cooled cake, spread the filling, and re-roll without the towel. Trim edges for a clean look.

Frost the Cake: Spread the chocolate frosting over the rolled cake. Use a fork to create a log texture.

Decorate: Dust with powdered sugar and add berries and rosemary for a festive look.