Proceed by adding a ladle full of hot broth as the rice cooks, and stirring it constantly to cook evenly as well as to prevent hardening of the rice and sticking to the bottom of the pot. After 15 minutes add half the broth with the dissolved saffron. When the rice begins to dry out, add the rest of the broth with saffron. When the saffron broth has been absorbed, continue cooking the risotto with hot broth. At this time, add the mushrooms as well.
Correct heat is important in making risotto.
A low simmer is ideal. Risotto is ready when the rice is tender and moist but al dente. When the rice is done, tender but al dente, firm to the bite, taste for salt. Usually the beef broth has sufficient salt for taste. Add a few twists of pepper to taste, and turn off the heat.