Steps
1. Preheat your oven to 350°F (175°C) and line a small baking sheet with parchment paper.
2. In a bowl, whisk the egg and granulated sugar until pale and frothy.
3. Gently fold in the flour, cocoa powder, and melted butter until just combined.
4. Pour the batter onto the prepared baking sheet and spread it evenly.
5. Bake for 10-12 minutes, until the cake is set. Allow it to cool slightly.
6. Meanwhile, whip the heavy cream, powdered sugar, and vanilla extract until soft peaks form.
7. Once the cake is cool, carefully invert it onto a clean kitchen towel and peel off the parchment paper.
8. Spread a layer of the whipped cream evenly over the cake.
9. Roll the cake tightly from one end, using the towel to help, and place it seam-side down.
10. Dust with cocoa powder and decorate as desired before serving.