Stir fry onion in oil, until golden.
Add rice and stir fry for 1-2 minutes. When it begins to stick to the pan, add wine.
When this has evaporated, add broth, one ladleful at a time when the previous one has almost all evaporated. Half way dilute the saffron in broth and keep adding as described. Stir constantly, until rice is cooked (about 25-30 minutes).
Salt, add butter and parmesan and serve hot right away. In Italy they say that "rice waits for no one", meaning that it soon overcooks if kept waiting. The North-American variety,long grain (Big Ben),is much more time tolerant.
Sprinkle with abundant parmesan.