Bottom Layer: Melt ½ cup unsalted butter, ¼ cup white sugar, and 5 tbsp cocoa over medium heat. Add 1 beaten egg and stir to cook and thicken. Remove from heat. Stir in 1¾ cups graham wafer crumbs, ½ cup slivered almonds, and 1 cup unsweetened coconut. Press into an ungreased 9×13 pan and chill.
Middle Layer: Cream together ½ cup unsalted butter, 2 tbsp + 2 tsp cream (or milk), 2 tbsp vanilla custard powder, and 2 cups icing sugar. Beat until light. Spread over bottom layer and chill.
Top Layer: Melt 4 squares semi-sweet chocolate and 2 tbsp unsalted butter over low heat. Cool. When cool, but still liquid, pour over second layer and chill.
Keep in refrigerator.