In a large pan, melt 2 tablespoons of butter over medium heat. Add the onion and cook until soft.
Add the rice and stir to coat it with the butter. Cook for 2 minutes.
Pour in the wine and cook until it has evaporated.
Add a ladle of warm broth and stir until absorbed. Continue adding broth, one ladle at a time, stirring constantly until the rice is creamy and cooked through.
Dissolve the saffron in a little warm broth and add it to the rice.
Stir in the remaining butter and Parmesan cheese. Season with salt and pepper.