French Onion Ground Beef & Rice Casserole

Preheat the oven to 375°F (190°C).
In a large skillet, heat olive oil or butter over medium heat. Add the sliced onions and cook for 15 to 20 minutes, stirring frequently, until deeply golden and caramelized. Remove from skillet and set aside.
In the same skillet, add the ground beef. Cook until browned, breaking it up as it cooks. Add the minced garlic and cook for another minute. Season with salt, pepper, and dried thyme.
Stir in the uncooked rice, beef broth, Worcestershire sauce, and half of the caramelized onions. Mix well to combine.
Pour the mixture into a greased 9×13-inch baking dish, spreading it out evenly.
Top with the remaining caramelized onions, then sprinkle the mozzarella (or Gruyère) and Parmesan evenly over the top.
Cover the dish with foil and bake for 30 minutes. Remove the foil and bake for an additional 10 to 15 minutes, or until the cheese is bubbly and the rice is fully tender.
Let the casserole rest for about 5 minutes before garnishing with fresh parsley and serving warm.

Vegetarian Option: Swap ground beef for sautéed mushrooms or lentils for a meatless version with equally rich flavor.
Cheese Upgrade: Use Swiss, Fontina, or Emmental in place of mozzarella for different flavor profiles.
Spicy Twist: Add a pinch of red pepper flakes or a dash of hot sauce to the beef mixture for a little heat.
Make It Creamy: Stir in a half cup of sour cream or cream cheese with the beef for a creamier texture.

Take your time with caramelizing the onions—low and slow heat develops the best flavor.
Use freshly grated cheeses for the best melt and texture.
If your rice isn’t quite done after the initial bake, cover again with foil and return to the oven for an extra 5–10 minutes.
This casserole can be prepped ahead and stored in the fridge for up to 24 hours before baking. Add 10–15 minutes to the bake time if baking from cold.