Catfish resonates classic American comfort food, its whiskers as ubiquitous with Southern cuisine as a beaded glass of sweet iced tea on a summer day. Versatility and taste make certified, farm-raised catfish a widely consumed fish. You can cook catfish as you do any other fish, but it really shines when you keep it simple – cooked in a cast-iron skillet with a side of sautéed onions. The cast-iron skillet makes cooking catfish and onions simple. You can fry the onions on the stove, add your catfish and pop the whole thing straight in a roaring-hot oven – not much time or cleanup needed.
Move the oven rack to the middle position. Heat the oven to 500 degrees Fahrenheit with the convection fan on, if it has one.
Pour 1 cup of panko breadcrumbs, 1 cup of cornmeal and 1 teaspoon of kosher salt in a mixing bowl or food storage bag for every whole catfish or for every two catfish fillets you're cooking. Mix the breading in the bowl using a whisk, or shake the food storage bag, if you used one. Spread the breading in an even layer on a plate.
Beat 2 large eggs and 2 tablespoons of milk or cream in a bowl for every whole catfish or for every two catfish fillets, using a whisk. Pour the egg wash in a shallow dish.
Place a whole catfish or catfish fillets on a wire rack set on top of a sheet pan and pat dry with paper towels. Season the catfish on both sides to taste.
Pour enough oil with a high smoking point, such as grape seed, canola or peanut, into your cast-iron skillet to thickly coat it. Set the skillet on a stove set to medium-high and let the oil heat until shimmering.
Dip the whole catfish or each fillet in the egg wash to coat it on all sides while the oil heats. Place the whole catfish or the fillets in the breading and gently press with you fingers. Turn the catfish over and repeat. Coat the sides of the catfish with breadcrumbs, and return them to the rack on the sheet pan.
Add a whole onion, cut into 1/3-inch-wide slices, for each catfish or every two fillets to the skillet. You can use any type of onion, depending on your tastes, just slice them evenly.
Fry the onions until limp, but not browned, and turn the heat off. Stirring the onions frequently with a wooden spoon while they fry helps prevent browning. Move the onions to the sides of the pan so you have room to place the whole catfish or the fillets between them.
Position the whole catfish or fillets between the onion pieces in the cast-iron skillet. Gently press the fish to ensure uniform contact with the skillet. Place the skillet on the center rack in the oven.
Cook the catfish until golden brown on the bottom, about 5 or 6 minutes. Pull the oven rack out enough to turn the catfish over safely. Drizzle oil on the top of the fish.
Stir the onions with a wood spoon and gently turn the catfish over with a slotted spatula. Turn the catfish over in the direction facing away from you, so if the oil splatters it does so in the opposite direction.
Push the skillet back in the oven and cook until the other side browns up golden on the bottom, about 5 or 6 minutes. Remove the skillet from the oven and place it on a cooling rack or pan.
Remove the catfish from the skillet and place it on a plate lined with paper towels until service. The skillet will continue cooking the fish if you leave it in. Insert a meat thermometer in the side of the catfish and make sure it’s at least 145 degrees F.