Melt the butter in a saucepan over medium heat. Add the onion and sauté for 10 minutes.

Add the rice and toast it for 2 to 3 minutes, stirring constantly.

Pour in the hot vegetable broth and cook the rice. After 5 minutes, dissolve the saffron in a little hot broth and add it to the rice.

Continue adding broth and stirring until the rice is fully cooked, about 20 minutes total.

At the end of cooking, stir in the butter and grated cheese vigorously. Serve hot.