Preheat oven to 375°. Heat oil in an ovenproof large skillet over medium-high heat. Season chicken thighs with salt and pepper. Place chicken, skin side down, in hot skillet and cook for 8 minutes or until browned. Flip chicken over and cook 3 minutes. Remove chicken and set aside on a serving plate. Remove all but 2 tablespoons of fat from skillet. Add shallots and cook, stirring constantly, for 1 minute. Add chicken broth, white wine and vinegar and bring to a simmer, scraping up all browned bits from bottom and sides of skillet. Place chicken back in skillet, skin side up and bake, uncovered, until chicken registers 195°, about 35-40 minutes. Remove chicken from skillet, place on a serving plate, and cover with foil. Place skillet over high heat and whisk in tomato paste and bring to a boil. Cook, stirring and scraping the sides of the skillet until the sauce is thickened and reduced to 1¼ cups, about 5-7 minutes. Remove from heat, whisk in the cold butter and chopped tarragon. Season with salt and pepper. Pour the sauce around chicken. Serve and enjoy. Profitez de manger!