In a medium saucepan, heat the chicken broth so that it is warm, if not gently simmering.
Coat another medium saucepan with olive oil, add the onion and celery, and heat on medium. Cook the mixture until it is cooked, and the onions are translucent (but not coloured).
Add the arborio, and stir constantly until they are coated with the oil and veg mixture. The rice will become translucent.
Add the wine, and stir, stir, stir, until the wine has just about disappeared.Add the saffron and a ladle-full of hot broth. Stir, stir, stir.
When the broth is absorbed, add another ladle-full. Continue until the risotto is al dente (or as cooked as you like it). The risotto will look thick and creamy.
Add the butter and as much or as little of the grated parmesan cheese as you like. The risotto will thicken even more and become even creamier.