Place corned beef, fat side up, and contents of spice packet in a large Dutch oven; cover with water, and bring to a boil over medium-high heat. Cover, reduce heat, and simmer 2 hours and 45 minutes or until fork-tender.
Skim and remove fat from surface; add cabbage, and return to a boil over medium-high heat. Reduce heat, and simmer 15 more minutes or just until cabbage is tender. Serve with Creamy Lemon Horseradish Sauce.
Corned Beef, Cabbage, Potatoes, and Carrots: Simmer corned beef as directed in Step Skim fat, and add 1 lb. small red potatoes, halved, and 8 oz. baby carrots. Bring to a boil over medium-high heat; reduce heat, and simmer 10 minutes. Add 1 lb. cabbage, coarsely chopped, and simmer 15 more minutes or until vegetables are tender. Prep: 20 min.; Cook: 3 hr., 30 min.