Heat the butter in a pan. Sauté the onion and garlic. Add the rice and sauté until translucent, stirring constantly. Pour in the wine and reduce almost completely. Add the saffron, gradually add the stock, stirring frequently, so that the rice is always just covered with liquid. Simmer for approx. 20 mins. until the rice is creamy and al dente. Stir in the parmesan and butter, season.