Put the stock in a saucepan and keep at a gentle simmer. Melt half the butter in a large, heavy saucepan and add the onion. Cook gently for 10 minutes until soft, golden and translucent but not browned. Add the rice and stir until well coated with the butter and heated through. Pour in the wine and boil hard until it has reduced and almost disappeared. This will remove any raw alcohol taste.

Begin adding the stock, a large ladleful at a time, stirring gently until each ladle has almost been absorbed by the rice. The risotto should be kept at a bare simmer throughout cooking, so don’t let the rice dry out – add more stock as necessary. Continue until the rice is tender and creamy, but the grains still firm. (This should take 15–20 minutes depending on the type of rice used.)

Taste and season well with salt and pepper, then stir in the remaining butter and all the Parmesan. Cover and let rest for a couple of minutes so the risotto can relax and the cheese melt, then serve immediately. You may like to add a little more stock just before you serve, but don’t let the risotto wait around too long or the rice will turn mushy.