01 - Prepare the catfish fillets by thoroughly patting them dry with paper towels. Evenly brush both sides of each fillet with olive oil.
02 - In a small bowl, combine all specified ingredients for the blackening spice mix. Stir well to ensure an even blend.
03 - Evenly sprinkle the prepared spice mix over both surfaces of each catfish fillet, gently pressing to ensure adherence.
04 - Heat a large cast iron skillet over medium-high heat until it is very hot and just begins to smoke, typically 2 to 3 minutes.
05 - Carefully place the seasoned catfish fillets into the hot, dry skillet. Cook for 3 to 4 minutes per side, or until the fish is opaque throughout and flakes easily with a fork. Cook in batches if necessary to avoid overcrowding the pan.
06 - While the catfish cooks, melt the unsalted butter in a small saucepan over low heat. Stir in the lemon zest, fresh lemon juice, and finely chopped fresh parsley. Remove from heat immediately.
07 - Transfer the cooked catfish fillets to individual serving plates. Drizzle generously with the prepared lemon butter sauce and, if desired, garnish with additional fresh parsley. Serve immediately.