"This rich, old-fashioned oyster stew is shared in memory of my mother, Ramona M. Filipek (1928 to 2006).
It is a Christmas family favorite, but good anytime. Serve hot with oyster crackers. Leftovers can be frozen."
Melt butter in a 10-quart stockpot over medium-high heat. Cook and stir celery, fresh onion, dried onion, black pepper, and celery salt in melted butter until celery and onion are tender, 7 to 10 minutes.
Reduce heat to low. Sprinkle flour over celery and onions; stir gently until flour becomes a smooth paste. Add the cream of celery soup; stir gently. Pour 1% milk, condensed milk, and liquid from the oysters into the mixture; stir. Gently fold oysters into the soup.
Increase heat to medium. Cook mixture at a simmer, stirring occasionally, for 1 hour. Remove from heat and allow to cool slightly, about 10 minutes.
Refrigerate soup for 24 to 48 hours before reheating gently to serve.