Heat oil in a medium saucepan over medium heat for 1 minute. Cook onion until translucent, about 3 minutes.
Add rice and a pinch of salt. Sauté until rice is translucent, 1 to 2 minutes.
Add wine and saffron; bring to a simmer, stirring, until rice has absorbed most of wine.
Add 2 ladles of stock to rice; simmer, stirring, until rice has absorbed most of stock. Continue adding stock, allowing rice to absorb it before adding the next ladleful. Cook until rice is al dente and mixture is a little loose. Stir in butter. Turn off heat. Stir in grated cheese. Cover and let sit 2 minutes. Divide among 4 bowls.