Grease and line the base and sides of a 23cm x 33cm non-stick flat roll tin with baking paper.
Melt the chocolate in a heatproof bowl over some barely simmering water, until just melted. Set aside and allow to come to room temp.
Separate the eggs into two separate bowls. Whisk the egg whites until stiff peak stage.
In the second bowl, add the sugar to the egg yolks and whisk on high for 2 to 3 minutes until thick and pale in colour.
Pour the melted chocolate into the yolk mixture and fold in to combine
Add 2 large spoonful’s of whisked egg white and stir in to loosen the mixture.
Gently fold in the remaining egg whites using a metal spoon, being careful not to knock the air out from the whites.
Sift in the cocoa powder and fold it in
Pour the mixture into the tin and bang on the side to evenly distribute
Pop in the oven and bake for 20-25 minutes or until risen. Remove and cool in the tin; the sponge will fall a little as it cools
Lay a large piece of non-stick baking paper on the worktop and dust it lightly with icing sugar. Turn the sponge out onto the paper, then carefully peel off the lining paper
Whip the cream for the filling until just holds its shape, then spread it over the sponge, leaving a clear edge of about 2cm on all sides. Then, using a sharp knife, make a shallow cut along one of the short edges
Roll this cut edge over tightly to start. Use the sugar-dusted paper to continue tight rolling by pulling it away from you as you roll. Finish with the join underneath.
Lift the roulade onto a serving plate or board using a large wide spatula or 2 fish slices. Cut into slices and enjoy!