Preheat oven to 200 C. Beat yolks and sugar together until pale and creamy, mix in cocoa and cornflour. Beat whites in a separate bowl until peaks form but don't let the egg white dry.
Gently fold the whites into the yolk mixture. Pour mixture into a lined Swiss roll pan and bake for 10-15 minutes until puffed and springy. Gently turn warm souffle out onto a baking paper lined surface, roll the souffle with the baking paper in between. Wrap in a tea towel and allow to cool. Once cool, unroll souffle and then cover with whipped cream and raspberries if using and roll again. Dust with icing sugar or cocoa to serve.