Combine all of the ingredients (except beef and cabbage) in a large slow cooker, stirring until well- blended; top with the beef.
Cover the slow cooker and cook on high for 8 hours (or on low for 11 hours) or until the beef is tender. Place the cabbage wedges into the slow cooker 1½ hours before the cooking time ends. Remove the cabbage wedges and place into a serving bowl. Remove the beef to a cutting board, and cut across the grain into thin slices.
Discard the broth (or strain it and make a gravy out of it); serve the beef with whole- grain mustard and wedges of cabbage.