How to Make It
Halve each chicken breast lengthwise to form 4 cutlets. Place each cutlet between 2 sheets of heavy-duty plastic wrap, and flatten to 1/4-inch thickness, using a rolling pin or flat side of a meat mallet. Discard plastic. Sprinkle salt and pepper over both sides of chicken. Place flour in a shallow dish, and stir in chopped thyme and rosemary. Dredge chicken in flour mixture; shake off excess. Cook 2 cutlets in 4 1/2 tsp. hot oil in a large skillet over medium-high heat 2 to 3 minutes on each side or until done. Remove cutlets from pan, and repeat procedure with 4 1/2 tsp. oil and remaining 2 dredged cutlets. Add remaining 1 Tbsp. oil to drippings in skillet; add mushrooms, and sauté over medium-high heat 4 to 6 minutes or until browned and all moisture evaporates. Stir in vinegar, and cook, stirring occasionally, 1 to 3 minutes or until liquid evaporates. Stir in broth and sage; bring to a boil. Boil until liquid is reduced to about 1/4 cup. Remove from heat; stir in mustard. Whisk in butter, 1 Tbsp. at a time. Spoon sauce over cutlets.