Melt a knob of butter and a tbsp of olive oil in a pan, then add the chopped onion. Add the tomatoes and, after 5 minutes, the rice. Stir well and after a few minutes add the wine. Let it evaporate on a high heat. Lower the heat and cook the rice adding the vegetable stock one ladle at a time. When almost cooked, add the cheese (previously cut into strips), salt, pepper and nutmeg. Stir well and serve. This rice should be very soft.