Heat wine to simmering in small skillet and simmer 1 minute. Stir in saffron and remove from heat. Let stand.
Heat 2 T. butter and the oil in large saucepan over low heat. When butter foams, stir in onion and cook until tender and golden, about 15 minutes.
Meanwhile, pour broth into small saucepan. Heat until hot and keep hot over very low heat.
Add rice to onion, increase heat to medium, and cook, stirirng constantly, until edges of grains are transparent, about 5 minutes.
Pour enough broth into rice to cover by 1/4 inch. Adjusting heat to maintain a lively simmer (not steady boil), simmer, stirring constantly, until liquid is absorbed and you can see bottom of pan as you stir, about 5 minutes.
Add more broth to cover rice by 1/4 inch and continue to simmer, stirring constantly, until liquid is absorbed. Repeat adding broth and simmering until rice is tender but still slightly girm at the center; it should take about 20 minutes from time first liquid is added. Season to taste and with salt and pepper halfway through cooking.
Stir wine mixture into risotto. There should be enough liquid to make rice creamy; if not, add more broth. Remove from heat and stir in remaining 2 T. butter and the Parmesan. Taste and adjust seasonings. Serve hot.