Position oven racks in upper and lower thirds of oven. Heat oven to 350°F. Place Corned Beef Brisket in roasting pan; sprinkle garlic, contents of seasoning packet and peppercorns around and over brisket. Add water; cover tightly with aluminum foil. Braise in upper third of 350°F oven 3 to 3-1/2 hours or until brisket is fork-tender.
Meanwhile, place butter, green onions, horseradish, ground pepper and salt in glass measuring cup. Microwave on HIGH 1 to 2 minutes or until butter melts; mix well. Place cabbage wedges on 1 half of baking sheet and potatoes on other half. Drizzle remaining horseradish-butter mixture over vegetables, turning cabbage and tossing potatoes to coat. Cover with aluminum foil. Roast in lower third of 350°F oven with brisket 55 minutes. Uncover vegetables; continue roasting 15 to 20 minutes or until vegetables are tender and begin to brown.
Combine glaze ingredients in small bowl. Remove brisket from roasting pan; place on rack in broiler pan so surface of brisket is 3 to 4 inches from heat. Brush glaze over brisket; broil 2 to 3 minutes or until glaze is bubbly and beginning to brown.
Carve brisket diagonally across the grain into thin slices. Serve remaining brisket and potatoes with cabbage.
Nutrition information per serving: 568 Calories; 306 kcal Calories from fat; 34 g Total Fat; 16 g Saturated Fat; 12 g Monounsaturated Fat; 129 mg Cholesterol; 1344 mg Sodium; 44 g Total Carbohydrate; 9.3 g Dietary Fiber; 22 g Protein; 4.1 mg Iron; 2.9 mg NE Niacin; 0.3 mg Vitamin B6; 1.4 mcg Vitamin B12; 4.4 mg Zinc; 29.7 mcg Selenium;