Wash apples; remove core, leaving apples whole. Fill center of each apple with about 2 tablespoons peanut butter, packing gently. Wrap each tightly in plastic wrap. Refrigerate until filling is set, about 30 minutes.
Cut each apple crosswise into 1/2-inch-thick slices. Divide slices into 4 portions; wrap each portion tightly in plastic wrap. Refrigerate until serving time.