Simply made skillet supper - ready in half an hour.
Sprinkle one side of chicken with salt and pepper. Heat a large skillet over medium heat until hot. Add half of butter and swirl to coat pan. Add chicken breasts, seasoned-side down, and season remaining side. Brown on both sides. Transfer to a plate and over with foil to keep warm.
Melt remaining butter in skillet. Cook potatoes, onions and rosemary, stirring, for 2 minutes or until some liquid is released. Cover, reduce heat to medium and cook, shaking pan often, for about 15 minutes or until potatoes and onions are almost tender and starting to brown. Increase heat and add vinegar. Boil, scraping up any bits stuck to pan, until reduced and syrupy. Pour in stock and bring to a boil. Return chicken to pan with any accumulated juices, spooning some of the sauce over chicken. Cover, reduce heat and simmer for about 10 minutes, until potatoes are tender and chicken is no longerr pink inside. Transfer chicken to serving plates. Season sauce and vegetables with salt and pepper to taste and spoon over chicken. Garnish with fresh rosemary sprigs.