Bring the milk and creams to the boil with the vanilla pod, add the rice and sugar, then stir well.
Tip the rice into the prepared dish, then grate a little nutmeg over the top. Dot with knobs of butter, bake for 15 mins, lower the oven to 160C/fan 140C/gas 3, then bake for 1 hour more, by which time the pudding should be golden brown on top and creamy underneath.