- STEP 1
Preheat the oven to 200 degrees Celsius.
- STEP 2
Sit a large heatproof bowl over a pan of simmering water, add the eggs and sugar and whisk for 5-10mins or until the mixture is thick and creamy.
- STEP 3
Sift in the flour and cocoa powder and fold in gently with a metal spoon.
- STEP 4
Line the Swiss roll tin with baking parchment, then pour mixture into the tin and level the top. Bake for 10mins or leave sponge is springy to the touch.
- STEP 5
Remove from the oven, cover with a damp tea towel and leave to cool on a wire rack.
- STEP 6
Put the butter into a mixing bowl and beat with an electric hand whisk until creamy. Then add a little at a time of icing sugar, then whisk. Then put cooled sponge onto some greaseproof paper to help you, spread the mixture over the sponge and roll up, starting from one of the short sides. Dust with more cocoa powder (if needed) and serve.