Ingredients

• 3 tablespoons butter
• 1 onion, thinly sliced
• 1 pound skin-on fresh cod
• 1 tablespoon seasoned salt, or more to taste
• 1/2 cup mayonnaise
• 2 1/2 tablespoons grated Parmesan cheese
• 2 1/2 tablespoons shredded provolone cheese
• 2 1/2 tablespoons shredded mozzarella cheese
• 1 tablespoon chopped fresh parsley

Instructions

1. Preheat oven to 400 degrees F (200 degrees C). Place butter in a 9x13-inch casserole dish.
2. Place casserole dish in the preheating oven until butter is melted, about 5 minutes.
3. Spread onion slices in the bottom of the casserole dish. Place cod skin-side down over onion. Sprinkle seasoned salt evenly on top.
4. Mix mayonnaise, Parmesan cheese, provolone cheese, mozzarella cheese, and fresh parsley together in a bowl. Spread over cod.
5. Bake in the preheated oven until cod flakes easily with a fork, 20 to 25 minutes.