Source: All Time Favorites, Slow Cooker by Better Homes and Gardens
1 (2- to 3-pound) corned beef brisket with spice packet
1 cup water
1/3 cup Dijon-style mustard
2 teaspoons prepared horseradish
4 cups coarsely shredded cabbage
8 Kaiser rolls, split and toasted
Trim fat from meat. If necessary, cut meat to fit into slow cooker. Sprinkle spices from packet evenly over meat; rub in with your fingers.
Place meat in a 3 1/2- or 4-quart slow cooker.
In a small bowl combine water, the 1/3 cup mustard and horseradish. Pour mustard mixture over meat. Top with cabbage.
Cover and cook on the LOW heat setting for 8-10 hours or on HIGH for 4-5 hours.
Transfer meat to a cutting board. Thinly slice meat across the grain. Arrange slices on bottom of rolls.
Use a slotted spoon, to place some of the cooked cabbage on top of the corned beef slices. Spread more mustard on roll tops. Replace roll tops.