Cream 4 oz margarine and 4 oz caster sugar. Add in two beaten eggs, 2 dessertspoons coffee essence, 2 dessertspoons milk. Mix in 6 oz plain flour, 2 teaspoons baking powder and 2 oz chopped walnuts. Beat well and divide between two 7 inch sandwich tins. Bake in a moderate oven. When cool sandwich together with coffee butter cream - 4 oz icing sugar, 2 oz butter and a dessertspoonful of coffee essence. Spoon on top and sprinkle with halved walnuts.