STOVE TOP: Place brisket fat-side up in a large pot and cover it with water. Bring the water to a boil; then reduce the heat and simmer, allowing about one hour per pound. Vegetables may be added during the last 20 to 30 minutes of cooking. Cook to desired tenderness.
SLOW COOKER: If using root vegetables, put them in the bottom of slow cooker. Cut brisket into pieces of like size to ensure thorough cooking. Place brisket on top of vegetables (if using) or in bottom of cooker. Add about 1-1/2 cups of water or enough to cover meat. Cover and cook on high setting for the first hour of cooking. Then cook for 10 to 12 hours on the low setting or 5 to 6 hours on high. Cabbage wedges may be added on top of the brisket during the last three hours of cooking.
MICROWAVE: Calculate cooking time at 20 to 30 minutes per pound. Place brisket in a large casserole dish and add 1-1/2 cups of water. Cover with lid or vented plastic wrap and microwave on medium-low (30 percent power) for half the estimated time. Turn meat over and rotate dish. Microwave on high for remainder of time or until fork tender. Vegetables may be added during the final 30 minutes of cooking.
Some consumers prefer to cook corned beef ahead of time. It is easier to cut uniform slices when corned beef is cold. Cooking ahead also makes it easier to reheat and serve later.
After cooking a whole corned beef, cut it into several pieces for faster cooling -- or slice it, if you like. Place the beef in small, shallow containers and cool it in the refrigerator quickly.
Any corned beef left over from a meal should be refrigerated promptly -- within two hours of cooking or reheating. Use cooked-ahead or leftover corned beef within 3 to 4 days or freeze up to 2 months.