Preheat your oven to 350°F (175°C). Line a jelly roll pan with parchment paper and grease lightly.

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

In another bowl, beat eggs until pale and frothy (about 3 minutes). Add melted butter, milk, and vanilla; mix until smooth.

Gently fold the egg mixture into the dry ingredients until just combined.

Pour batter into the prepared pan and bake for 12-15 minutes or until a toothpick comes out clean.

Immediately turn the cake onto a powdered sugar-dusted kitchen towel. Peel off parchment and roll it up in the towel while warm. Let it cool completely.

Unroll the cooled sponge gently, spread your choice of filling (like whipped cream or ganache), then roll it back up carefully. Dust with powdered sugar before slicing.