Drain oysters, reserving liquor. Inspect oysters and remove any bit of shell. Set aside oysters and liquor.

In medium saucepan heat milk and cream just to simmering; keep warm.

In Dutch oven heat 4 tablespoons of the butter over medium heat. When butter is melted and bubbling, add onion, celery, and 1/2 teaspoon of the salt, stirring well to coat in butter. Cook slowly, about 10 minutes, stirring often until onion is tender and translucent. Sprinkle flour over vegetable mixture. Cook 2 minutes more, stirring well to blend in the flour. Slowly whisk in the hot milk and cream; ring mixture back to a low simmer, stirring occasionally.

Meanwhile, in a 12-inch nonstick skillet heat remaining 3 tablespoons butter over medium heat until hot and bubbly. Add drained oysters in a single layer. Sprinkle remaining salt and a few grinds of black pepper. Cook just until oysters begin to curl around the edges and gills are slightly exposed. Transfer oysters to the milk mixture in Dutch oven. Turn off heat.

Add oyster liquor to hot skillet. Cook 2 to 3 minutes, until liquor comes to boiling. Immediately transfer to stew in Dutch oven; stir. Sprinkle cayenne and stir in. Cover and let stand for 10 minutes. Sprinkle servings with parsley.