In a shallow dish or zip-top bag, combine the buttermilk, hot sauce, Cajun seasoning, and sea salt.
Add the catfish fillets, making sure they are completely submerged. If using a zip-top bag, make sure the excess air is pressed out. Cover and refrigerate for 1 hour; soaking much longer can soften the fish's texture so I don't recommend it.
Prepare the Coating
In a separate shallow dish, combine the cornmeal, flour, Cajun seasoning, garlic powder, onion powder, sea salt, and black pepper.
Remove the catfish from the buttermilk, allowing the excess to drip off. Place each fillet in the seasoned cornmeal mixture and press the coating onto both sides, making sure the entire surface is covered without bare spots.
Place the coated fillets on a plate or wire rack and let them rest for 5 minutes before frying.
Fry the Catfish
Add ½–¾ inch of oil to a heavy-bottomed skillet and heat to 350°F for the first batch.
Carefully add the coated catfish without overcrowding the skillet. The oil temperature will drop when the fish is added. Adjust the heat as needed to maintain approximately 325°F while frying.
Fry for approximately 4–5 minutes per side, depending on thickness, until the coating is deeply golden brown and crispy and the fish reaches an internal temperature of 145°F.
Transfer the cooked catfish to a wire rack set over a baking sheet. Allow it to rest briefly before serving.
Continue frying the remaining fillets in batches, allowing the oil to recover to approximately 340°F before adding the next batch.
Notes
Soak time: Keep the fillets submerged for 1 hour; soaking much longer can soften the delicate fish.
Extra-large fillets: If you have only 2 fillets per pound, the coating may brown before the center reaches 145°F. Finish in a 350°F oven, or use an air fryer oven (mine took about 5 minutes at 400°F without preheating). Cooking time depends on thickness.