Cake: In a bowl, beat butter, egg yolk and sugar. Add flour with baking powder and cocoa then mix well.
Line a round cake tin with baking paper. Add 2/3 of the dough and smooth down. Put the rest of the dough in the freezer.
Coconut Layer: Beat the egg whites with the sugar the same way you would make a meringue. Gently fold in the coconut, then spread over the chocolate layer in the cake tin.
Crumble or grate the remaining dough over the coconut layer. Preheat oven to 180 degrees C and bake cake for 1 hour. Let cool.
Custard Cream: Beat the egg yolks with the sugar and vanilla. Add 50ml cold milk and stir. Add the flour and mix well. Add 50ml more cold milk and mix.
Bring the remaining milk to a boil and pour in a thin stream into the yolk mixture, stirring well. Return to the saucepan and cook over medium heat, stirring with a wooden spatula, until thickened. Add 30g butter and remove from the heat. Let cool to room temperature, stirring occasionally.
Beat the rest of the softened butter until light. Add two tablespoons of the custard and continue beating. Add brandy, vanilla and the rest of the custard. Spread over the top of the cake and refrigerate overnight.
Chocolate Glaze: Melt the chocolate and butter together in a double boiler, let cool slightly. then pour evenly over the cake. Decorate as desired.