1. Begin by caramelizing the onions. Heat butter in a skillet over medium-low heat, add sliced onions, and season with a pinch of salt. Stir to coat the onions in butter and cook slowly for 15-20 minutes until they become golden brown and develop deep sweetness.

2. While the onions are caramelizing, prepare the rice. Substitute water with beef broth when cooking for added flavor. Follow package instructions, and once finished, set the rice aside to cool slightly.

3. In a large mixing bowl, combine the cooked rice, caramelized onions, canned cranberry sauce, canned French onion soup, and shredded Gruyère cheese. Carefully fold the mixture until all ingredients are combined evenly. Taste and adjust seasoning with salt and pepper as needed.

4. Preheat your oven to 350°F (175°C). Transfer the mixed ingredients into a baking dish, smoothing out the top with a spatula.

5. Cover the baking dish with aluminum foil to prevent the mixture from drying out. Bake in the oven for 20 minutes.

6. After 20 minutes, remove the foil and continue baking the dish for another 10 minutes, allowing the top to become slightly crisp.

7. For added flavor enhancements, consider experimenting with optional ingredients like sautéed mushrooms, crispy fried onions, alternative cheeses, or fresh herbs such as rosemary or thyme.

8. Serve the dish warm as an indulgent Thanksgiving side, or experiment with pairing it alongside roasted meats or additional holiday classics.

9. To store leftovers, refrigerate in an airtight container for up to two weeks or freeze for up to six months. Reheat gently on the stove to maintain texture and flavor.