Process 3/4 cup pecans, flour, and 1 teaspoon Creole seasoning in a food processor until finely ground; place pecan mixture in a large shallow bowl, and set aside.
Whisk together egg and milk in a large bowl, and set aside.
Sprinkle both sides of fillets evenly with remaining 1/2 teaspoon Creole seasoning.
Dip catfish fillets in egg mixture, draining off excess; dredge fillets in pecan mixture, coating both sides, and shake off excess.
Melt 2 tablespoons butter in a large nonstick skillet over medium heat until butter starts to bubble. Place 2 fillets in skillet, and cook 2 to 3 minutes on each side or until golden. Drain on a wire rack in a jellyroll pan, and keep warm in a 200° oven. Wipe skillet clean, and repeat procedure with remaining fillets.
Wipe skillet clean. Melt remaining 1/2 cup butter in skillet over high heat; add remaining 3/4 cup pecans, and cook, stirring occasionally, 2 to 3 minutes or until toasted. Squeeze juice from lemon halves into skillet; place halves cut side down in skillet. Stir in Worcestershire sauce, thyme, salt, and pepper, and cook 30 seconds or until thyme wilts and becomes very aromatic. Remove and discard lemon halves and wilted thyme.
Place fish on a serving platter; spoon pecan mixture over fish. Garnish, if desired.