Peel the onions and chop them finely. I use a food processor for this. Peel the mushrooms and rinse them quickly under running water. Never keep mushrooms in a bowl of water, they will soak up the liquid and turn soggy. Wash the parsley and chop it finely.
Heat the olive oil in a pan with high walls. Fry the onions on low heat until they turn translucent, and then add the rice without washing it. Keep on stirring for about two minutes until the rice is evenly coated with the oil-onion mixture.
Add the first cup of stock and rise the temperature to medium. Keep on stirring until the liquid bubbles, and then add the second cup of stock. Some chefs recommend heating the stock, but I keep on forgetting this. In my kitchen cold stock works just as well, it just takes a little longer. When the rice mixture turns thick, add the third cup of stock.
Slice your mushrooms and add them to the risotto. Keep on incorporating the liquid until you have used all the stock. At this point I have to tell you a secret. Most times I go against the rules and add all my stock in the beginning. I let it simmer for about five minutes before I incorporate the mushrooms. However, this is not the proper way to do it (although I have never noticed any difference). A risotto cooked in this way would probably not satisfy a real chef. My men never complained.
All in all the risotto takes 18 to 20 minutes for cooking. During this time you have to keep on stirring occasionally to prevent it from sticking to the pan. Shortly before the end of the cooking time, add the chopped parsley. You can keep a bit of parsley to decorate the risotto when you serve it. Once the grains are soft but still have a bit of bite, remove the pan from the heat. Stir in the butter which you have diced. Then add half of the grated cheese and stir until your risotto has a rich, creamy texture. It should flow but not ooze out excess liquid.
Serve it immediately with the rest of the grated cheese. Enjoy!