Melt butter in 2-quart pot over medium heat. Add onions and cook covered, stirring occasionally, 10 minutes or until onions are tender. Add mushrooms, replace cover and continue to cook another 10 minutes. Add Sherry, thyme, salt and pepper to taste. Sprinkle onion mushroom mixture with flour and cook, stirring, about 1 minute. Add milk and cream, cover and simmer additional 10 minutes. Do not let soup come to rolling boil or milk will curdle. Serve piping hot soup immediately. Makes 6 servings. soup 28