Season the chicken generously with salt and pepper and set aside.

Add 1-2 tablespoons of olive oil to an oven safe skillet (with a lid) over medium-high heat. When the pan is hot, turn to medium heat and add the chicken thighs skin side down. Cook until the skin is golden brown, about 5-7 minutes. Flip the chicken and cook for another 5 minutes and then remove the chicken to a plate or bowl and set aside.

Keep the pan at medium heat and add the butter. Once the butter is melted, add the thinly sliced shallots, pearl onions and thinly sliced yellow onion. Add the sugar and salt and stir to combine. Cover and cook for 5 minutes, undisturbed. Then remove the lid and turn to medium-low heat. Cook the onions, stirring occasionally (so they don't burn), until golden brown and caramelized, about 20-25 minutes.

While the onions cook, preheat the oven to 350F.

When the onions are caramelized, turn the heat to medium. Pour in the wine and deglaze the pan, scraping up any browned bits and cook until most of the liquid has evaporated. Add the minced garlic, beef base, Worcestershire sauce, dried thyme, ground pepper and rice and stir to combine, making sure the rice is coated with the seasonings. Add in the bay leaf and hot water and bring to a simmer. Once simmering, add the chicken back on top of the rice along with any juices from the plate / bowl back to the pan as well.

Cover the skillet with a lid or aluminum foil and transfer to the preheated oven and bake until cooked through to 165F, about 30-35 minutes.

Once the chicken is cooked through, remove from the oven and fluff the rice a bit with a fork - remove the bayleaf.

Sprinkle all of the gruyere cheese and parmesan over the chickens and rice. Broil for 1-2 minutes in the oven until the cheese is melted.