Crumble the madeira cake and add to the bowl of an electric mixer and turn on to break to a crumb. Add in the vanilla and enough of the cream cheese whilst mixing to form a thick dough. Add in the sprinkles and mix in. Press the mixture into a lined 8 inch square tin and flatten out. Place into the freezer for 45 minutes. When ready, remove from the freezer and cut into diamonds or squares. Carefully dip into the melted chocolate, tap off any excess and decorate the top with extra sprinkles. Allow to set before serving.