Rinse fish and pat dry. In shallow dish, combine flour, cornmeal, onion salt, and pepper; set aside. Melt butter in shallow dish. Roll cod in butter, then in flour mixture. Place fillets in 8-inch square baking dish. Drizzle remaining butte over fillets and top with grated parmesan cheese. Bake in a 450 degree oven for 12 to 14 minutes or until cod flakes easily when tested with fork.
