8 frozen potato and onion pierogies
2 (3/4 inch) thick bone-in pork loin chops
1/2 teaspoon salt, divided
1/2 teaspoon pepper, divided
4 tablespoons butter, divided
1 medium sweet onion, sliced and separated into rings
1 Golden Delicious apple, cut into 1/4 inch slices
1/4 cup sugar
1/4 cup cider vinegar