Clean, then cut the smaller mushrooms in half, and quarter the larger ones. Once cooked, they will shrink considerably. Heat a skillet to medium heat. Add in the butter and olive oil, once melted add in the mushrooms.
Sauté for at least 8-10 minutes (stirring ofteor until you have developed some good color on them, this is key! If you cook them for less time, you won't get the same amazing flavor, so don't rush them! First, they will seem dry, but as they continue to cook, they will start to give up their liquid.
Once most of the liquid has evaporated, make a well in the center of the pan and add in the garlic. Sauté for about 20 seconds, be careful not to burn it. Deglaze the pan with the white wine, scraping up those brown bits of flavor.
Add in the salt and pepper and continue cooking for another 5 minutes or until most of the wine has evaporated. Stir in the parsley and serve on the side of a steak, chicken, pork or whatever you like.