A cheesy, buttery casserole of sweet onions baked until tender and melty—perfect as a side or topping.

Units Scale

3–4 large sweet onions (Vidalia or similar), sliced into 1/4‑inch rounds and separated into rings
4 Tbsp unsalted butter, cut into pats
1/2 tsp salt
1 tsp garlic powder
1/2 tsp dried oregano
1/2 tsp dry mustard
1/4 tsp cayenne pepper (optional)
1 cup shredded mozzarella cheese
1 cup sharp cheddar cheese, shredded
1/2 cup grated Parmesan cheese

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Preheat oven to 350 °F (175 °C). Grease a 9×13‑inch baking dish with non‑stick spray.
Peel onions and slice crosswise into ¼‑inch rounds. Separate rings (leave 2‑3 rings attached if needed).
Arrange onion rings evenly in baking dish.
In a bowl, whisk salt, garlic powder, oregano, mustard, and cayenne. Sprinkle over onions and gently toss.
Dot onions with butter pats evenly.
Sprinkle mozzarella and cheddar over onions, then top with Parmesan.
Cover dish with foil and bake 35–40 min until onions are tender and cheese is melted.
Uncover and bake another 5–10 min until cheese is bubbly and golden.
Serve hot (or warm); delicious on its own or as a topping for burgers, grilled meats, sandwiches.