Submerge corned beef, fat side up, in water in a larger pot. Cover and simmer over low heat until beef is tender when pierce with a fork (3-3.5 hours).
Preheat oven to 450. Line the baking sheet with foil, top with a cookie cooling rack. Transfer the cooked beef to the prepared rack, fat side up. Use a knife to trim off the fat.
Whisk remaining ingredients together in a saucepan and bring to a boil over high heat until thickened (3-4 minutes). Spoon glaze onto beef, then roast (10 minutes or until the glaze is dark and sticky). Remove from oven and let meat rest (15 minutes).
Transfer to a cutting board, then thinly slice against the grain.
mark.goadrich