For Caramelizing Onions:

2 large yellow onions, thinly sliced

2 tablespoons butter

1 tablespoon olive oil

Salt and pepper, to taste

For the Ground Beef Mixture:

1 pound lean ground beef

1 cup uncooked long-grain white rice

1 can (10.5 oz) condensed cream of mushroom soup

1 cup beef broth

1 teaspoon Worcestershire sauce

1/2 teaspoon garlic powder

1/2 teaspoon dried thyme

1/2 cup shredded cheddar cheese (plus extra for topping)

Optional Additions:

1 cup frozen peas and carrots

Fresh parsley, chopped (for garnish)

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Preheat oven to 350°F (175°C) and grease a 9×13-inch baking dish.
In a large skillet, melt butter and olive oil over medium heat. Add sliced onions and a pinch of salt. Cook 20–25 minutes, stirring occasionally, until onions are golden and caramelized. Set aside.
In the same skillet, brown ground beef over medium-high heat until fully cooked. Season with salt and pepper and drain excess fat if needed.
Add uncooked rice, cream of mushroom soup, beef broth, Worcestershire sauce, garlic powder, thyme, and half of the caramelized onions. Stir to combine.
Mix in frozen peas and carrots if using.
Transfer mixture to the prepared baking dish and spread evenly.
Top with shredded cheddar cheese and remaining caramelized onions.
Cover tightly with foil and bake for 40–45 minutes, until rice is tender and casserole is bubbly.
Remove foil, sprinkle extra cheese on top, and bake uncovered for 5–10 more minutes until melted and golden.
Let rest a few minutes before serving. Garnish with fresh parsley.

Use Gruyère or Swiss cheese for a more authentic French onion flavor.

For added richness, stir in a few tablespoons of sour cream before baking.

Brown rice can be used—add 15 minutes and 1/2 cup more broth.

Add a splash of sherry or wine while caramelizing onions for deeper flavor.

Freeze before or after baking for easy make-ahead meals.