Preheat the oven to 350°F (175°C) and line a jelly roll pan with parchment paper.

In a bowl, whisk together flour, cocoa powder, sugar, and baking powder.

In another bowl, beat eggs until frothy; add vanilla and mix well.

Gently fold dry ingredients into the egg mixture until just combined. Spread batter evenly in the prepared pan.

Bake for 12-15 minutes or until a toothpick comes out clean. Let cool completely.

While cooling, whip heavy cream with powdered sugar and cocoa until soft peaks form.

Carefully unroll the cooled cake, spread the filling evenly, then roll it back up using parchment as a guide.