Blend tarragon, rosemary and pepper. Coat chicken breasts with herb mixture. In large skillet, over medium heat, saute chicken in 1 tbsp margarine for 4-5 minutes on each side or until done. Remove from skillet; keep warm.
In same skillet, over medium heat, saute shallots in remaining margarine for 1-2 minutes or until tender. Add vinegar; cook for 1 minute. Stir in broth and sugar; heat to a boil. Reduce heat. Simmer until sauce is reduced by 1/3. Stir in mustard. Blend cornstarch into water, stir into skillet. Heat until mixture thickens and begins to boil. Serve sauce over chicken.
