1. HEAT the cream in a small saucepan and bring just to the boil. Remove from the heat immediately then pour over the finely chopped chocolate and whisk vigorously to combine. Set aside to firm for 2 hours at room temperature. Refrigerate the ganache if necessary until firm enough to spread.
2. BEAT together the butter and sugar until light and fluffy. Add the egg and vanilla and beat well. Add the sifted flour and cocoa, and the milk and beat just to combine. Stir through half of the extra chopped chocolate.
3. SPOON into 12 x 1/3 cup capacity patty paper lined muffin pans. Bake in a moderate oven 180°C for 20 minutes or until cooked when tested. Cool on a wire rack for 10 minutes before turning out of pan to cool completely. Spread each of the cakes with the prepared hazelnut ganache then top with remaining chocolate to serve.