Generously season the chicken breasts with salt and pepper on both sides.

Heat 1 tablespoon of olive oil in a large oven-safe skillet over medium-high heat. Sear the chicken for 3-4 minutes on each side until golden brown. Remove to a plate and set aside.

In the same skillet, reduce heat to medium-low and add butter. Add thinly sliced yellow onions with a pinch of salt. Cook for 20-25 minutes, stirring occasionally, until deeply caramelized.

Stir in minced garlic and fresh thyme. Cook for about 30 seconds until fragrant.

Pour in the rinsed rice and stir for 1 minute to toast slightly, coating it with the onion mixture.

Pour chicken broth into the skillet and bring to a simmer. Return the chicken to the pan, nestling it into the rice mixture. Cover and reduce heat to low, cooking for 18-20 minutes until the rice is tender and the chicken reaches 165°F.

Remove the skillet from heat and preheat your broiler. Sprinkle grated Gruyère or Swiss cheese evenly over the chicken and rice.

Place the skillet under the broiler for 2-3 minutes until the cheese is bubbly and golden brown. Watch it closely to prevent burning.

Finish with freshly chopped parsley if desired. Let the dish rest for 5 minutes before serving.