Ingredients

· 4 eggs, separated

· 1 teaspoon vanilla extract

· 260 g caster sugar

· 110 g unsalted butter, melted

· 75 g plain flour, sifted

· 35 g cocoa powder, sifted

· 500 ml lukewarm milk

· Chocolate curls, to decorate

Method

Preheat the oven to 160°C. Grease a cake pan and line with baking paper. Place egg whites in a mixer and whisk to stiff peaks. Transfer to a bowl and set aside. By using the paddle attachment, beat the egg yolks, vanilla and sugar until thick and pale. Add butter and beat for one minute. Add flour and cocoa, and, with the motor running, slowly add milk until combined. In batches, fold in egg white. Pour into prepared pan and bake until set with a slight wobble in the centre. Set aside to cool, then chill for four hours to firm. Scatter with chocolate curls and dust with cocoa powder to serve.