In a separate pan, heat butter and olive oil. Add chopped onion and cook gently until translucent. Stir in the arborio rice and cook 1 or 2 minutes until lightly toasted.
Pour in the wine and let it reduce. Add stock one ladle at a time, stirring constantly. Let the rice absorb each ladle before adding more.
After 10 minutes, stir in saffron with its soaking water. Continue cooking and stirring for about 18 to 20 minutes total, or until the rice is al dente and creamy.
Stir in grated Parmesan and season to taste. Add a touch more butter for richness.
