In a medium saucepan, bring the lamb or chicken stock to a simmer; keep warm. Put 1/4 cup of warm stock in small container with saffron.
In a large saucepan, heat the olive oil. Add the onion, season with salt and pepper and cook over moderate heat, stirring, until softened, about 5 minutes.
Add the rice and cook for 1 minute, stirring to thoroughly coat. Add the stock with the saffron to the rice. Add the wine.
Cook, stirring, until the wine is absorbed. Add 1 cup of the warm stock and cook over moderate heat, stirring constantly, until nearly absorbed.
Continue adding the stock 1/2 cup at a time, stirring constantly, until it is nearly absorbed between additions.
The risotto is done when the rice is al dente and suspended in a thick, creamy sauce.
Season the risotto with salt and pepper. Stir in the cheese, butter (optional) and parsley and serve immediately.