Cook pierogi according to package directions. Meanwhile, sprinkle pork chops with 1/4 teaspoon salt and 1/4 teaspoon pepper. In a large skillet, cook chops in 2 tablespoons butter over medium heat until juices run clear; remove and keep warm.
In the same skillet, saute onion in remaining butter for 3 minutes. Add apple; saute until almost tender. Stir in the sugar, vinegar, and remaining salt and pepper. Bring to a boil. Reduce heat; simmer, uncovered, for 5 minutes. Drain pierogi. Add pork chops and pierogi to skillet; stir to coat.