Combine corned beef, sauerkraut, broth, onion, garlic, caraway seeds and peppercorns in Crock-Pot slow cooker. Cover; cook on LOW 7 to 9 hours.
Remove beef to large cutting board. Cut beef across grain into slices. Divide among 4 bread slices. Top each slice with drained sauerkraut mixture and 1 slice cheese. Spread mustard on remaining 4 bread slices; place on sandwiches. Serve with chips, if desired.