For bottom layer: Put butter, sugar, cocoa and vanilla in top of double boiler and melt. Stir in beaten egg. Add graham cracker crumbs, coconut and nuts. Press in square layer pan 9x9. For middle layer: Mix together cream, custard powder, sugar and butter and spread over bottom layer. Refrigerate for at least 1/2 hour. Top layer: Melt together chocolate and butter, and spread over middle layer when chocolate mix has cooled slightly. Store in refrigerator. Recipe can easily be doubled and put in a 9 x 13 pan. Cookies are somewhat thicker this way.