Heat 50 g (2 oz) of the butter in a saucepan, add the rice and cook gently for 2 minutes, stirring. Heat the milk in a separate saucepan, pour about one-third over the rice and add the spice.
Cook the rice gently for 40–50 minutes, stirring occasionally until the rice is tender and creamy, topping up with ladlefuls of milk as the rice swells and stirring more frequently towards the end of the cooking time.
Remove the rice from the heat and stir in the sugar. Heat the remaining butter in a frying pan, add the grapes and fry for 2–3 minutes until hot. Spoon the risotto into shallow bowls, top with spoonfuls of crème fraîche, then spoon the grapes and a little extra spice on top. Serve immediately.