Start with the crust. Melt together the butter, brown sugar, and cocoa.

I did mine over a double boiler, but if I had a microwave, I probably would have done it that way.

Beat the egg, and quickly whisk it into the hot chocolate mixture. You need to add the egg slowly and keep the whisk moving, otherwise you will have scrambled eggs. Not good.

Mix in the graham crackers, coconut, and walnuts.

Press the crust into an 8×8 pan that has been lined with parchment. Put the crust into the fridge to chill for a half hour.

Make the buttercream layer, but creaming together the powdered sugar, butter, and custard powder. Add the cream slowly, and beat until light and fluffy, about 5 minutes.

Spread the cream layer evenly over the crust. Back in the fridge for another half hour or so.

Melt together the butter and chocolate (either a double boiler or microwave) and pour over the chilled cream layer.

Back in the fridge to set up.

Cut into small squares (they are really rich) and keep in the fridge.