Spicy Cider Corned Beef

3 medium onions, sliced
1 small head cabbage, cut into wedges
4 pounds corned beef brisket
1/4 cup packed brown sugar
1 cup apple cider
2 teaspoons grated orange peel
2 teaspoons mustard
6 whole cloves
1 jar spiced apple rings

Place onions and cabbage in crock pot. Trim fat from brisket, place meat atop vegetables. Stir together cider, brown sugar, orange peel, mustard and cloves, pour over meat. Cover, cook on low-heat setting for 8-10 hours. Garnish platter with apple rings. Pass mustard, if desired.