Preheat the oven to 350°F (175°C) and line a jelly roll pan with parchment paper.
Prepare the chocolate sponge batter by whisking the eggs and sugar until light and fluffy, then gently fold in the flour and cocoa powder.
Spread the batter evenly into the prepared pan and bake for 10–12 minutes until the cake springs back when touched.
Turn the warm cake onto a clean kitchen towel dusted with powdered sugar and gently roll it up. Allow it to cool completely.
Unroll the cake and spread an even layer of chocolate whipped cream filling.
Carefully roll the cake back into a tight log and refrigerate for at least 1 hour.
Dust with cocoa powder or drizzle with chocolate ganache before slicing and serving.