Add 1 cup of the hot stock to the rice and cook, stirring constantly, until almost all the stick has been absorbed. Add the tomato halves, garlic and another cup of stock and cook, stirring until the stock is absorbed. Continue to add hot stock, 1 cup at a time, stirring until it is absorbed before adding more. The risotto is done when the grains are just tender and bound with a creamy sauce, about 25 minutes in all. Stir in the butter and Parmesan, season with salt and pepper and serve.