1. Stir together 1/4 cup apple juice, 1 Tbsp. brown sugar, and mustard in a large zip-top plastic freezer bag; add pork. Seal bag, and shake well to coat. Chill 30 minutes, turning once. Remove pork from marinade, discarding marinade. Pat pork dry, and sprinkle with 1/2 tsp. salt and 1/2 tsp. pepper.
2. Cook pork in hot oil in large skillet over medium-high heat 3 minutes on each side. Remove chops from skillet.
3. Cook onion and garlic in hot drippings, stirring constantly, 1 minute. Add remaining 3/4 cup apple juice to skillet, stirring to loosen particles from bottom of skillet. Stir in rosemary, 1 Tbsp. brown sugar, 1 Tbsp. balsamic vinegar, and remaining 1/2 tsp. salt and pepper.
4. Bring onion mixture to a boil. Reduce heat to medium low, and simmer 3 to 5 minutes or until mixture is reduced by half.
5. Add pork to onion mixture, turning to coat. Cover and cook 5 to 10 minutes or until a meat thermometer inserted in thickest portion registers 155°. Remove from heat, and place pork on a serving platter. Cover with aluminum foil. Let stand 5 minutes.
6. Meanwhile, whisk together 1/4 cup water, 1 Tbsp. flour, remaining 1 1/2 Tbsp. brown sugar, and remaining 1 Tbsp. balsamic vinegar in skillet until smooth. Bring to a boil over medium-low heat. Reduce heat to low, and simmer 1 to 2 minutes or until slightly thickened and bubbly. Drizzle sauce over pork, or serve with pork, if desired. Garnish, if desired.