I've had this recipe for years and it's become a firm favourite in our village cafe, making a really dark, chocolatey, moist cake. I suppose you could use Guinness instead, but I have a fond loyalty to the less popular stout!
Sift flour, baking powder, bicarb and cocoa together.
Cream sugar and margarine until light, beat in eggs, then alternatively, fold in flour and 200ml Mackeson stout.
Divide between two base lined and greased 7" sandwich tins.
Bake for about 30 minutes until just springy.
For the icing, melt the chocolate, then beat in the sifted icing sugar, butter and Mackeson. Use about 3/4 to sandwich the cake and the rest to ice the top and finish off with chopped walnuts.