1To make the tarter sauce, combine all the ingredients in a small mixing bowl, whisk well, then set aside
2Heat 2 inches of oil in a large skillet or a deep fryer to 350 F. Combine the cornmeal, pepper, salt, granulated garlic, an onion powder on a large plate and mix well. Rinse the fillets, then lightly dust them with the seasoned cornmeal.
3Dredge through the buttermilk, then lay one side in the cornmeal mixture and press lightly to make sure the cornmeal sticks. Flip and press the other side. Gently lay each fillet in the hot oil and cook for 2 to 3 minutes, then flip and cook for 2 to 3 minutes longer or until the coating is crunchy and the fish is cooked thoroughly.
4Remove the fillets and drain on paper towels., then serve with the tarter sauce on the side. In Mississippi, it's also traditional to serve catfish with a slice of yellow onion or a whole scallion.