Rinse shrimp and pat dry. Cut catfish into 3–4" strips and pat dry. In a shallow bowl combine buttermilk, hot sauce, 1 tsp kosher salt and 1/2 tsp black pepper. Submerge shrimp and catfish in the buttermilk mixture, cover and refrigerate for 20–30 minutes (up to 2 hours for more flavor).

Breading / Batter

Make breading

In a wide, shallow dish whisk together flour, cornmeal, 1 tsp salt, paprika, garlic powder, onion powder, cayenne (if using) and baking powder. Mix thoroughly so spices are even.

Dredge seafood

Remove seafood from buttermilk, allowing excess to drip off. Working in batches, press each shrimp and catfish piece into the dry mixture, coating completely. Shake off excess and set on a wire rack. For a thicker crust, dip back briefly into buttermilk and re-coat in the dry mix (double-dredge).

Fries

If using fresh potatoes: cut into 1/4–1/2" sticks, rinse in cold water to remove starch, then pat dry thoroughly. Heat oil in a deep skillet or fryer to 325°F (160°C). Blanch fries in two batches for 3–4 minutes until soft but not browned. Remove and drain on paper towels. Increase oil temperature to 375°F (190°C) and fry fries until golden and crisp, 2–4 minutes. Drain on paper towels and season with 1 tsp salt. If using frozen fries, cook according to package directions (usually 350–400°F) until crisp and season with salt.

Frying / Finish

Heat 1"–2" of oil (about 1 cup in a heavy skillet) or enough in a deep fryer to reach 350–360°F (175–180°C). Test the oil by dropping a pinch of flour — it should sizzle immediately. Fry the breaded catfish pieces in batches so they don't overcrowd the pan: cook 3–4 minutes per side until golden brown and cooked through (internal temp for fish 145°F/63°C). Shrimp will cook faster — about 2–3 minutes until golden and opaque. Remove fried seafood to a wire rack set over a baking sheet to keep crisp. If necessary, keep in a 200°F (95°C) oven while finishing remaining batches.

Finish and serve: Sprinkle chopped parsley over the seafood if using and serve with lemon wedges. Plate with fries and a small bowl of tartar sauce on the side.

Tartar Sauce (optional)

While seafood marinates, combine mayonnaise, chopped dill pickle or relish, lemon juice, Dijon mustard, chopped parsley and black pepper in a small bowl. Taste and adjust salt or lemon as needed. Chill until serving.