1Season chicken on both sides with salt and pepper. Heat 1½ teaspoons oil in a large heavy skillet over medium-high heat. Add the chicken and sear until well browned, about 3 minutes per side. Transfer the chicken to a plate and tent with foil.
2Reduce heat to medium. Add the remaining 1½ teaspoons oil to the pan. Add shallots and garlic. Cook, stirring, about 1 minute. Add orange juice and broth; bring to a simmer. Cook until reduced by half, about 3 minutes.
3Return the chicken and any accumulated juices to the pan; reduce heat to low. Simmer until the chicken is cooked through, about 4 minutes. Transfer the chicken to a warmed platter. Stir butter, rosemary and vinegar into the sauce. Season with salt and pepper and spoon over the chicken.