In a medium bowl, beat the softened butter and granulated sugar until creamy.
Mix in the cocoa powder until fully incorporated.
Add the graham cracker crumbs and shredded coconut, stirring until combined.
Press the mixture into the bottom of a greased 8x8 inch pan.
In another bowl, whisk together the custard powder, powdered sugar, and milk until smooth.
Spread the custard mixture evenly over the crust in the pan.
In a saucepan, melt the chocolate and butter together over low heat.
Once melted, pour the chocolate over the custard layer, spreading it evenly.
Chill the bars in the refrigerator for at least 2 hours until set.
Once set, cut into squares and serve chilled.