At home, as Jugglering said, it's not really worth cooking risotto in advance as it takes so little time to prepare. But in professional kitchens we do par-cook the risotto in advance, and then finish it to order. This is done in a few different ways depending on what type of finished risotto is required, but most commonly a base risotto will be made by sweating onion/shallot, maybe garlic, and the rice, and adding white wine followed by the appropriate type of stock. The risotto is prepared in the normal way, adding a little stock at a time, but only cooked until just before 'al dente'. It is then cooled and used as required when an order comes on.