Ready your oven for baking at 350°F (175°C).
Put the olive oil and butter in a big pan and set it over medium heat. Cook, stirring periodically, the sugar and thinly sliced onions until the onions caramelize and develop a golden brown color. Estimated time required: fifteen to twenty minutes.
In a greased 9×13-inch baking dish, distribute the uncooked rice evenly while the onions caramelize.
Season with salt and pepper and add the beef stock to the pan when the onions have caramelized. After thoroughly mixing, reduce heat to a low simmer.
Once the rice is properly coated in the baking dish, pour the onion and broth mixture over it.
Put the baking dish in the preheated oven and cover it with aluminum foil. Bake for 30 minutes.
Return to the oven after 30 minutes, remove foil, and top with shredded Gruyère cheese. To get melted and bubbling cheese, bake, uncovered, for another 15 minutes.
To make sure all the flavors combine, take it out of the oven and let it alone for a few minutes before serving.

Tips and Variations
Swapping out the beef stock for veggie broth will make it suitable for vegetarians. For a more rustic taste, try sautéing some mushrooms. Furthermore, add some crispy fried onions on top of the meal just before serving if you’re a crunch fan.

Ready your oven for baking at 350°F (175°C).
Put the olive oil and butter in a big pan and set it over medium heat. Cook, stirring periodically, the sugar and thinly sliced onions until the onions caramelize and develop a golden brown color. Estimated time required: fifteen to twenty minutes.
In a greased 9×13-inch baking dish, distribute the uncooked rice evenly while the onions caramelize.
Season with salt and pepper and add the beef stock to the pan when the onions have caramelized. After thoroughly mixing, reduce heat to a low simmer.
Once the rice is properly coated in the baking dish, pour the onion and broth mixture over it.
Put the baking dish in the preheated oven and cover it with aluminum foil. Bake for 30 minutes.
Return to the oven after 30 minutes, remove foil, and top with shredded Gruyère cheese. To get melted and bubbling cheese, bake, uncovered, for another 15 minutes.
To make sure all the flavors combine, take it out of the oven and let it alone for a few minutes before serving.

Tips and Variations
Swapping out the beef stock for veggie broth will make it suitable for vegetarians. For a more rustic taste, try sautéing some mushrooms. Furthermore, add some crispy fried onions on top of the meal just before serving if you’re a crunch fan.