1. In a heavy bottomed pot, heat the olive oil and 2 tablespoons of the butter over medium heat.
2. Add the onion and cook until softened and translucent, 8 to 10 minutes.
3. Add the saffron and cook, stirring, for 1 minute.
4. Add the rice and stir with a wooden spoon until the rice is well coated and opaque, 3 to 4 minutes.
5. Add the wine to the rice, and then add a 4 to 6 ounce ladel of simmering broth and cook, stirring occasionally, making sure to wipe the sides and bottom of the pot clean as you stir, until all the liquid is absorbed.
6. Continue adding the broth a ladle at a time, waiting until the liquid is completely absorbed before adding more.
7. After about 20 minutes begin to taste the rice.
8. It is ready when it is tender and creamy, but still a little firm to the bite.
9. Stir in the remaining 4 tablespoons of butter and the Parmagiano-Reggiano cheese until well mixed.
10. Transfer to serving plates and serve.