Brine chicken. Add chicken thighs and pickle juice (note 1) to a large resealable plastic bag. Press out any air, seal, and place in the fridge for at least 12 hours. (I like to nestle my bag inside a large bowl).
Saute. Preheat oven to 425 F. Add 1 tablespoon of olive oil to a large dutch oven, or oven-safe pan. Once shimmering, add the celery, carrots, and onions. Saute until softened (about 8 minutes). Add wine (note 2) , bay leaves, and peppercorns -- stir to combine. Add the chicken broth and chicken thighs (skin side down), making sure to fully submerge the thighs.
Braise. Bring liquid to a boil, then turn off the heat of the stove. Place dutch oven in the preheated oven (without a lid), and bake for 40 minutes. Once braised, remove from the oven, and crank the oven heat to broil.
Sauce. Set cooked chicken thighs aside on a plate. Strain the sauce using a mesh strainer nestled inside a large bowl. Discard the onions, celery, carrots, bay leaves, and peppercorn. Pour strained sauce into a small saucepan and bring to an aggressive simmer. Sprinkle xanthan gum (note 4) over the top while whisking at the same time to ensure it doesn't clump. Whisk until it fully dissolves into the liquid. Allow the sauce to simmer until it thickens to your liking (for me this was about 10 minutes), then keep warm while we cook the veggies.
Broil. Return chicken thighs, skin side up, to the dutch oven and broil until the skin becomes golden and crispy -- should be about 5 minutes, but you'll want to watch carefully, as they can burn easily at this temp. Once golden, remove from the oven and set aside on a plate. Tent with tin foil and allow the chicken to rest for 10 minutes.
Saute. Once cool enough to handle, use a paper towel to wipe clean the dutch oven. Add pancetta and saute for 4 minutes. Add the kale and garlic, season with salt. Cook over medium-high heat, tossing, until tender and the pancetta is crispy, about 5 minutes.
Plating. Spoon the kale onto plates and top with the chicken thighs. Drizzle sauce over your chicken and serve right away. Enjoy!