In the top of a double boiler, combine ½ cup softened butter, unsweetened cocoa powder, and granulated sugar. Stir occasionally until the mixture is melted and smooth. Add the beaten egg and continue stirring until the mixture thickens slightly, approximately 2 to 3 minutes. Remove from heat and immediately stir in the graham cracker crumbs, flaked coconut, and almonds. Press the mixture firmly and evenly into the bottom of an ungreased 8x8-inch square pan.

In a separate mixing bowl, beat together the remaining ½ cup softened butter, heavy cream, and custard powder until the mixture becomes light and fluffy. Gradually add the confectioners' sugar and continue to beat until smooth and spreadable. Evenly spread this custard filling over the chilled base layer. Refrigerate to set while preparing the chocolate topping.

Melt the semisweet baking chocolate together with 2 teaspoons butter, either using a double boiler or in the microwave at low heat, stirring at regular intervals until smooth. Pour the melted chocolate over the chilled custard layer and spread evenly with an offset spatula to cover the entire surface.

Allow the assembled bars to chill in the refrigerator until the chocolate topping is fully set. Once firm, cut into small squares using a sharp knife. For clean slices, wipe the knife between cuts.