How to make it

1. Preheat your oven to 350°F (175°C). Line a 10 x 15 in (25 x 38 cm) baking sheet with parchment paper.
2. In a bowl, sift together the flour, cocoa powder, baking powder, and salt.
3. In a large mixing bowl, beat the eggs and sugar on high speed until pale and thick, about 5 minutes. Stir in the vanilla extract.
4. Gently fold the dry ingredients into the egg mixture until just combined, being careful not to deflate it.
5. Spread the batter evenly onto the prepared baking sheet. Bake for 10-12 minutes until the cake springs back when lightly touched.
6. While the cake is baking, prepare a clean kitchen towel and dust it lightly with powdered sugar.
7. Once baked, immediately turn the cake onto the towel, peel off the parchment, and roll the cake up with the towel from a short side. Let it cool completely.
8. For the filling, whip the heavy cream, powdered sugar, and vanilla extract until stiff peaks form.
9. Unroll the cooled cake, spread the cream evenly over the surface, and roll it back up without the towel. Chill for 30 minutes.
10. Melt the chocolate chips and butter together in a microwave-safe bowl, stirring every 30 seconds until smooth.
11. Coat each roll with the melted chocolate and let set on a cooling rack. Chill for another 30 minutes to firm up the chocolate.