Orange(juice, grated rind) Preheat oven to 190ºC . Grease 2 8-9-inch cake pans. Cream the butter and sugar until light and fluffy. Sift the flour, baking powder, salt and cocoa into a bowl. Add the orange rind to the creamed butter and beat in the eggs, one at a time, including a spoonful of the measured flour mixture with each one, and beating well between additions. Gently mix in the Guinness, a tablespoonful at a time, including another spoonful of flour with each addition. If there's any flour left over, fold it in gently to mix; blend thoroughly without over-beating. Divide the mixture between the tins, smooth down, and put the cakes into the center of the preheated oven. Reduce the heat to moderate (350F) and bake for 35-40 minutes, or until the cakes are springy to the touch and shrinking slightly in the pans. Turn out and cool on a wire rack. . Meanwhile, make the icing. Cream the softened butter and icing sugar together thoroughly, then blend in the grated orange rind and enough juice to make an icing that is soft enough to spread. When the cakes are cold, use half the icing to sandwich them together, and spread the rest on top.