Put the mushrooms to soak for a couple of hours.
Grate the onion and crush the garlic. With half the butter cook the onion and the garlic. Pour the rice and cook a little. Then throw the wine and on medium heat let off evaporating the wine along with the rice, stirring often.
Add the mushrooms and cook with the rice. Saving some water from soaking them.
Always cook over medium heat. When there is almost no juice, we are adding ladles of broth (hot, inside the broth you will have mixed some of the water of the mushrooms). A couple of ladles each time and gone adding when you go thickening the rice.
Once you see that the rice is cooked (al dente, do not let it cook too much), remove the casserole from the fire and add the Parmesan cheese and the rest of the butter.
I recommend that you do not salt the rice as the Parmesan cheese is already a bit salty. Do not worry, it will remain al dente.