Grease an 8-in. sandwich tin, line the bottom with greaseproof paper. Blend the cocoa and hot water together and leave to cool Cream the margarine and sugar till very light; add the blended cocoa mixture. Beat in the eggs one at a time, adding a little sifted flour with the second. Fold in the flour, then the milk. Place in the tin, bake on the middle shelf of a preheated moderate oven (350° F., Gas 4) for 30–40 min. To make the icing: Cream the margarine with ½ the icing sugar until very light. Add remaining icing sugar with the milk and coffee essence. Beat until smooth and creamy. Roll out the almond paste thinly, cut into 10 triangles (1 in. wide and 3 in. long approx.). Make the remaining paste into balls. Leave to dry for 2–3 hr.
Spread the cake sides with icing and roll in chopped walnuts. Cover the top with icing and make a pattern with a fork. Decorate the top with the almond paste triangles and balls, the walnuts and remaining icing piped into stars.