On the stove-top, add to a large cast-iron pot (such as Lodge or Le Creuset), butter, corn oil and chicken thighs, skin-side down. Brown thighs on medium-high for about three minutes per side. Remove the thighs from the pot and set them aside.
Discard two-thirds of the pot oil mixture. Lower the temperature to medium, add all the vegetables, salt, pepper and sugar, and cook for about 10 minutes, stirring frequently. Add the tomato paste and stir. Add the sherry vinegar and stir.
Add chicken stock to the pot and bring it to a boil. Return the chicken thighs to the pot mixture and add thyme, bay leaves, herbs de provences, and return to a boil. Place the pot, uncovered, in the oven for 45 minutes. Serve immediately, or cool to room temperature. The cooked dish can be refrigerated for up to five days, or freeze for up to two months.
Recipe Notes
use an 18-inch “oven-safe” saute pan because the pan will eventually move from stove-top to oven.