Preheat the oven to 350°F (175°C). Line a 15x10 inch jelly roll pan with parchment paper and grease it lightly.

In a mixing bowl, beat the eggs with granulated sugar until thick and pale, about 5 minutes.

Add 1 teaspoon of vanilla extract, baking powder, and salt to the egg mixture, and mix until combined.

Sift together the flour and cocoa powder, then gently fold into the egg mixture until just combined.

Pour the batter into the prepared pan, spreading it evenly. Bake for 12-15 minutes or until the cake springs back when lightly pressed.

While the cake is baking, prepare a clean kitchen towel by dusting it with powdered sugar.

Once the cake is done, immediately invert it onto the prepared towel. Carefully peel off the parchment paper.

Starting from one short end, roll the cake up with the towel inside, creating a roll. Let it cool completely in this position.

In a separate bowl, whip the heavy cream with powdered sugar and 1 teaspoon of vanilla extract until stiff peaks form.

Unroll the cooled cake and spread the whipped cream evenly over the surface. Add a layer of mixed red and blue berries on top.

Roll the cake back up without the towel. Place seam-side down on a serving platter.

Dust the top with powdered sugar and garnish with additional berries for decoration.

Chill in the refrigerator for at least 1 hour before slicing and serving.