Melt 3 Tbsp of the butter in a heavy large saucepan over medium heat. Add the chopped onion, celery and carrot and saute until vegetables begin to soften, about 5 minutes. Mix in 2 tsp dry mustard. Add 1 1/2 cups canned chicken broth, potatoes, bay leaf, and thyme. Bring mixture to a boil. Reduce heat to low, cover saucepan and simmer until potaotes are almost tender, about 10 minutes. Add the corn and half and half. return soup to a simmer. Cover saucepan and cook until vegetables are tender, about 6 minutes. Reduce heat to very low and add the cheddar cheese to the soup, mixing until cheese is just melted. Season soup to taste with salt and pepper. Ladle soup into deep bowls, and garnish with remaining cheese and green onion and serve. From Bon Appetit; August 1991 Shared by Robert Rostrup