Bring the milk, sugar and vanilla to the boil in a pan, stirring constantly. Pour the mixture into a stainless steel bowl and leave to cool. Carefully fold in the whipped cream using a rubber spatula. Cover and freeze for approx. 2 hrs., stirring 2-3 times.
Place the chocolate in a thin-sided bowl and suspend over a gently simmering bain-marie, ensuring that the bowl does not touch the water. Melt the chocolate and stir until smooth. Mix the chocolate into the ice cream mixture using a fork, return to the freezer for approx. 1 hr.