Place the catfish fillets in a glass casserole dish and pour the buttermilk over them to soak 10 minutes. Place the breading in a shallow pan, and lift the catfish fillets out of the buttermilk and dredge on all sides in breading.

Meanwhile, heat 2 inches of vegetable oil to 365 degrees in a heavy pot. When the oil is hot, add two or three fillets of fish at a time, frying 2 to 3 minutes per side, turning over once, until browned and cooked through. Drain on a rack set over a sheet pan, and keep warm in a 200-degree oven until time to serve.

Fried Oysters: Repeat the same process with fried oysters, first soaking the shucked oysters in buttermilk and then dredging them in the breading before frying. Fry the oysters until golden brown, about 2 minutes.