Clean the mushrooms by scrubbing them with a small soft brush. Don’t wash or peel them unless absolutely necessary. Cut the mushrooms into bite size pieces.
Heat butter and oil in a large saucepan over high heat. Add the mushrooms and cook until they reabsorb all the natural juices they release during cooking. Add the garlic and continue to cook for another 2 minutes. Season generously with salt. Add white wine, dry sherry and sherry vinegar. Continue to cook until liquid is absorbed and mushrooms are a dark golden brown. Adjust seasoning and toss in chopped parsley.