PREP: Set up broiler so that fish will be 3 to 4 inches from cooking element. Preheat broiler for at least 30 seconds. Dry the haddock fillets with paper towels. Use a pastry brush to coat both sides of the filets with oil. Broil until cooked through. Fillets 1 inch thick should be done in 8 to 10 minutes. Dot fish with butter just before serving. VARIATION: When the fish is just about cooked through, lightly sprinkle the surface with 2-3 tablespoons of bread or cracker crumbs. Return the fish to the broiler, long enough to brown the crumbs.