Scald half-and-half in a large Dutch oven. Add butter, cracker crumbs, celery, salt, and pepper; mix well. Add oysters, a few at a time, to half-and-half mixture. Heat thoroughly. (Do not boil.) Pour into a 3-quart casserole. Bake, uncovered, at 350° for 30 minutes, stirring mixture at 15 minute intervals. Bake an additional 20 minutes, without stirring, to brown top. Ladle into individual soup bowls, and serve immediately. Serve with oyster crackers, if desired.