Mix butter, sugar and cocoa. Melt in a bowl set over hot water. Add beaten egg and mix thoroughly. Remove from heat. Add graham cracker crumbs, coconut, vanilla, and walnuts. Press firmly into an 8 by 8-inch pan. Place in refrigerator while mixing the next layer.
Second layer: Cream the butter, confectioners' sugar, and custard powder. Add small amount of milk. Beat until light and creamy. Spread on top of bottom layer. Place this in refrigerator for at least 20 minutes.
Topping: Melt chocolate and butter together in a bowl set over hot water. Mix well and spread on top. Chill in refrigerator.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.