Place buttermilk in a large zip-top plastic freezer bag; add catfish, turning to coat. Seal and chill 20 minutes, turning once.
Preheat oven to 425°.
Remove fish from buttermilk, discarding buttermilk. Sprinkle fish with Creole seasoning.
Place crushed cornflakes in a shallow dish.
Dredge fish in cornflakes, pressing cornflakes gently onto each fillet. Place fish on a wire rack coated with cooking spray in a roasting pan.
Bake at 425° for 30 to 35 minutes or until fish flakes with a fork. Serve immediately with lemon wedges.