200g plain chocolate, broken into cubes (we used Bournville)
200g dark muscovado sugar
175g butter, plus extra for greasing
3 eggs, separated
140g plain flour
1 tsp vanilla extract
zest 1 orange
200g tub soft cheese (I used Philadelphia Extra Light)
½ tsp vanilla extract
50g icing sugar
Heat oven to 180C/fan 160C/gas 4. Butter and line a traybake tin, 23 x 23cm or thereabouts. Put the chocolate, sugar and butter in a pan, then heat very gently for about 5 mins, stirring every min until the butter and chocolate have melted. Leave to cool for 10 mins. Beat in the egg yolks, flour, vanilla and half the orange zest.
Put the egg whites into a large, very clean bowl, then whisk until they stand up in peaks. Stir ¼ of the whites into the chocolate mix to loosen it, then carefully fold in the rest with a metal spoon. Pour the mix into the tin, then bake for 25 mins or until evenly risen and just firm to the touch. Cool in the tin, then cut into squares. Can be frozen for up to 1 month.
Beat together the cheese, vanilla, sugar and remaining zest until smooth. Spread over each chocolate square and serve. If you’re making ahead, spread the topping over just before serving.