Bottom: Mix the first quantity of butter, sugar and cocoa powder in a casserole. Bring slowly to boil. Add the egg stirring to thicken the mixture. Remove from the heat.
Incorporate the graham crumbs, walnuts and coconut. Press the mixture in a greased mold of 9 x 9 inch.
Middle: Mix second quantity of butter, milk, mint essence and icing sugar in a bowl. Beat well. Add green food coloring until you obtain a good green you like. Spread on the first mixture, in the mold.
Garnish: Melt the chocolate and the third quantity of butter in a casserole at low heat or above hot water (I did it in micro-waves) Spread on the second mixture in the mold. Put in the fridge. Keep in the fridge, covered.