Preheat the oven to 325°F
Remove the corned beef from the package and rinse it under cold water
Place the corned beef fat side up in a roasting pan
Add the seasoning packet if included
Add 1 to 2 cups of water, beef broth, or beer to the pan
Cover the pan tightly with foil or a lid
Roast for about 3 to 4 hours, or until tender
Check for doneness when the meat is fork-tender
Remove the foil during the last 15 to 20 minutes if you want a browned top
Let the corned beef rest for 10 to 15 minutes before slicing
Slice against the grain and serve