Ingredients
- 4 large sweet onions, peeled and sliced into ½-inch thick rings
- 2 tbsp olive oil
- 3 tbsp butter
- 3 tbsp all-purpose flour
- 2 cups heavy cream (or half-and-half for lighter version)
- 1 cup grated Parmesan cheese (divided)
- 1 cup shredded mozzarella cheese
- ½ tsp garlic powder
- ½ tsp salt (or to taste)
- ¼ tsp black pepper
- Fresh parsley, chopped (optional, for garnish)
Instructions
- Preheat Oven – Set to 375°F (190°C).
- Prepare Onions – Place sliced onions on a baking sheet, drizzle with olive oil, and toss to coat. Roast for 20–25 minutes until lightly golden and softened.
- Make Cream Sauce – In a medium saucepan, melt butter over medium heat. Whisk in flour and cook for 1–2 minutes until slightly golden. Slowly whisk in heavy cream, stirring constantly until thickened (about 5 minutes).
- Add Cheese & Seasoning – Stir in ½ cup Parmesan, mozzarella cheese, garlic powder, salt, and pepper until melted and smooth.
- Assemble Casserole – Transfer roasted onions into a greased baking dish. Pour the cheese sauce over the top, making sure onions are evenly coated. Sprinkle remaining ½ cup Parmesan over the surface.
- Bake – Place in oven for 20–25 minutes, or until bubbly and golden on top.
- Serve – Garnish with fresh parsley if desired, and serve warm as a side dish.
If you want, I can also give you a golden crispy topping variation so it has a gratin-style crunch. That would make it extra irresistible.