Chocolate mint Nanaimo bars are a delicious no-bake layered treat. Each bite is a tasty balance of texture and flavor featuring a soft minty custard middle sandwiched between chocolate and a coconut-graham crumb base.
Combine the butter, sugar, cocoa, egg and milk in a large sauce pan. Heat the mixture slowly over low heat stirring just until the butter melts and it becomes smooth. Remove from the heat quickly, just prior to all the butter melting.
Stir in the graham cracker crumbs, coconut and walnuts. Use a spatula to spread the base evenly into a 9 x 13 pan (see notes below.) Chill this layer for about 20 minutes.
Use a stand mixer or electric hand mixer. Combine the butter, milk, mint extract, custard powder, confectioner's sugar, drops of green food coloring and beat until it is smooth.
Use a spatula to spread this layer on top of the first. Chill for approximately 45 minutes.
Combine chocolate and oil together in a glass mixing bowl. Melt over a double boiler or in the microwave at half power for about 1 minute. Stir frequently just until it is almost completely melted. Remove from the heat and continue stirring until it is fully melted. Spread the melted chocolate over the custard layer and evenly distribute it using a spatula. Work quickly.
Chill the chocolate layer for about 30 minutes. Then using a sharp knife, score the chocolate where you will cut it into bars once it is completely set. Chill for at least another 30 minutes before cutting it into squares.