1. Slice 2-3 large onions thinly.
2. In a large skillet, melt 4 tablespoons of unsalted butter over medium heat.
3. Add the sliced onions to the skillet and cook slowly, stirring occasionally, for about 30-40 minutes until they turn a deep golden brown.
4. Season the onions with a pinch of salt and pepper to taste.
5. Preheat your oven to 350°F (175°C).
6. In a large mixing bowl, combine 2 cups of long-grain white rice, 1 can of condensed French onion soup, and 2 cups of beef broth.
7. Add 1/4 cup of melted unsalted butter to the rice mixture and stir well.
8. Season the rice mixture with salt and pepper to taste.
9. Grease a 9×13 inch baking dish with butter or cooking spray.
10. Pour the rice mixture into the prepared baking dish.
11. Spread the caramelized onions evenly over the top of the rice mixture.
12. Sprinkle 1 cup of grated Gruyère cheese over the onions.
13. Cover the baking dish tightly with aluminum foil.
14. Bake in the preheated oven for 30 minutes.
15. After 30 minutes, remove the foil and continue baking for an additional 20-25 minutes, or until the rice is tender and the cheese is golden brown and bubbly.
16. For an extra crispy top, broil the dish for 2-3 minutes at the end of the baking time.
17. Let the dish rest for 5-10 minutes before serving to allow the flavors to meld.