Combine 1/2 cup butter, sugar, and cocoa powder in a pot and on low, melting the butter and ingredients together. Stir occasionally until melted and smooth.
Whisk an egg in a separate bowl and then mix into the cocoa powder mixture until smooth. Stir for 2-3 minutes. It is important that you cook the cocoa mixture on low as to not "cook" the egg. Alternatively, you could "temper" the egg by putting spoonfuls of of the warm mixture into the whisked egg and then pour it all back into the mixture on the stove.
Take off the heat and mix in the graham crackers and coconut.
Press the mixture into the bottom of an ungreased 8x8 pan. Set aside or chill and move onto the Second Layer!
Cream together 1/2 cup butter, heavy cream, cornstarch, and vanilla until light and fluffy. Mix in the powdered sugar until smooth.
While the second layer is chilling, melt the semisweet chocolate and 2 teaspoons butter together over low heat.
The second layer is supposed to be a custard flavor and often many people don't have custard powder at their fingertips. Some people will substitute with vanilla pudding, but I like the cornstarch and vanilla approach better, it helps fluff up the icing!