Scrub and pierce potatoes. Bake at 350° for 65-75 minutes or until tender. Cool. Cut a thick slice off the top of each potato. Scoop out pulp, leaving a 1/4-in. shell. Transfer pulp to a bowl; add butter and mash. Stir in ham, onion and pepper. Spoon into potato shells. Bake, uncovered, at 350° for 20-25 minutes or until heated through.