In a mixing bowl, combine softened butter, granulated sugar, graham cracker crumbs, shredded coconut, and cocoa powder. Mix until well combined.

Press the mixture firmly into the bottom of a greased 9x9 inch baking pan.

In another bowl, beat together softened butter, powdered sugar, custard powder, milk, and vanilla extract until smooth and creamy.

Spread the custard mixture evenly over the base layer in the baking pan.

Melt the chopped chocolate and butter together in a double boiler, stirring until smooth.

Pour the melted chocolate over the custard layer, spreading it evenly.

Refrigerate the bars for at least 2 hours until set. Cut into squares and serve.