Butter or spray a 9 x 9 inch (23 x 23 cm) pan with a non stick vegetable spray.

Bottom Layer

1. In a saucepan over low heat, melt the butter. Remove from heat and stir in the sugar and cocoa powder and then gradually whisk in the beaten egg.
2. Return the saucepan to low heat and cook, stirring constantly, until the mixture thickens (1 - 2 minutes).
3. Remove from heat and stir in the vanilla extract, graham cracker crumbs, coconut, and chopped nuts.
4. Press the mixture evenly onto the bottom of the prepared pan. Cover with plastic wrap and refrigerate until firm (about an hour).

Middle Layer

1. In your electric mixer, or with a hand mixer, beat the butter until smooth and creamy.
2. Add the remaining ingredients and beat until the mixture is smooth. If the mixture is too thick to spread, add a little more milk.
3. Spread the filling over the bottom layer, cover, and refrigerate until firm (about 30 minutes).

Top Layer

1. Chop the chocolate into small pieces. Then, in a heatproof bowl, over a saucepan of simmering water, melt the chocolate and butter.
2. Spread the melted chocolate evenly over the filling and refrigerate for about 10 minutes or just until the chocolate has set.
3. Using a sharp knife, cut into squares.