Clean the mushrooms by removing the earth at the base of the stem, separating the cap from the stems and gently rubbing with a clean, damp cloth.
After cleaning the mushrooms, slice the cap and the stems.
In a rather large saucepan put to melt half the butter indicated, and then add the onion peeled and finely chopped and let it dry without making them take color; also add the rice and toast for two minutes, then add a ladle of broth and simmer over moderate heat, stirring and adding a little broth when needed.
In another pan of steel or non-stick material, place the oil and a clove of crushed garlic and brown for a few minutes ; then add the mushrooms, previosly cleaned and cut into slices.
Saute the mushrooms on full fire, adding half way trough cooking salt and at the end freshly ground pepper.also add, if necessary, a little vegetable broth to finish cooking (should last a maximum of 10-12 minutes total), then turn off the heat and, if you like, add 2 tablespoons of chopped parsley .Five minutes before the rice finishes its cooking, add the mushrooms, previously prepared, keep aside 2 tablespoons of mashroomsfor the garnish that will serve 4 dishes of risotto.
Once cooked, turn off the heat, add the grated Parmesan cheese and the remaining butter, stir well and leave it to rest for a while. At this point, divide the risotto in four portions and garnish the top of each with the mushrooms and serve immediately.Bring more grated Parmesan cheese at the table so that the guest if they wish they can add it.