Pat the thin-cut catfish fillets dry with paper towels. Trim any ragged edges so they sit flat. Place fillets in a shallow dish and pour the buttermilk mixed with hot sauce over them. Cover and refrigerate for 20–30 minutes (this tenderizes and helps the coating adhere).

Make seasoned flour

In a wide, shallow bowl or baking sheet, whisk together the all-purpose flour, cornmeal, salt, black pepper, paprika, onion powder, garlic powder, cayenne pepper, and baking powder until evenly combined. Taste (a pinch) and adjust seasoning if desired.

Dredge fish

Remove fillets from the buttermilk one at a time, allowing excess to drip off, then press each fillet firmly into the seasoned flour, coating both sides and the edges. Shake off any loose flour and place on a rack set over a sheet pan. For an extra-crispy coating, double-dredge: dip back briefly into buttermilk and into the flour again, pressing to build an even crust.

Frying and assembly

Heat oil

Pour oil into a heavy skillet or Dutch oven to a depth of about 1 to 1 1/2 inches (roughly 3–4 cups depending on pan). Heat over medium-high until oil reaches 350°F (175°C). If you don't have a thermometer, test with a pinch of flour: it should sizzle and brown slowly.

Fry the catfish

Working in batches to avoid crowding, gently lower coated fillets into the hot oil using tongs or a spider. Fry 2–4 minutes per side, depending on thickness, until deeply golden brown and internal temperature reaches 145°F (63°C). Adjust heat as needed to maintain 325–350°F so the crust cooks through without burning. Transfer fried fillets to a wire rack set over a sheet pan lined with paper towels to drain; sprinkle lightly with kosher salt while hot.

Make remoulade-style spread

While fish fries, stir together mayonnaise, Dijon mustard, and lemon juice in a small bowl. Taste and season with kosher salt and a little black pepper to taste. Optional: add a teaspoon of hot sauce or chopped pickles for more flavor.

Prepare rolls and assemble poboys

Slice the French bread or poboy rolls lengthwise, leaving a hinge if desired. Lightly toast the cut sides in a 400°F oven or on a skillet for 2–3 minutes until slightly crisp. Spread the mayonnaise mixture generously on both cut sides. Layer shredded lettuce, tomato slices, and pickles on the bottom half. Place a piece or two of the hot fried catfish on top, then finish with more lettuce if desired. Close the sandwich, press lightly, and slice in half.

Serve

Serve immediately while fish is hot and crispy. Provide hot sauce or lemon wedges on the side. Leftover fried catfish is best eaten the same day.