2. Arrange a rack in a casserole or Dutch oven.
3. Place the meat on the rack.
4. Cover with water.
5. Cover and transfer the casserole to the heated oven.
6. Cook corned beef for 2 ½ hours until almost tender.
7. Surround the meat with the vegetables and pour another ½ cup water over them if required.
8. Re-cover and return to oven for another half hour or so until meat and vegetables are cooked.
9. Transfer meat and vegetables to a platter.
10. Skim fat from pan juices, measure 1 ½ cups of it. Add to a saucepan.
11. Stir in gravy and prepared horseradish.
12. Simmer and cook stirring, until the sauce thickens.
13. Pour into a gravy boat.
14. Slice roast and serve with vegetables.
15. Pass gravy at the table.