Corned beef and cabbage has been used for years to celebrate St. Patrick's Day, but if you cook it well and trim it properly, it can make a healthy dish at any time and provide leftovers to fill sandwiches. Re-heating this dish can be difficult, though, as the meat may dry out and the cabbage may become limp and mushy. Make sure you have selected a good cut of corned beef brisket--if possible, buy a whole, raw one rather than one which has been partially cooked or cut into a smaller piece to ensure the best flavor.
Place corned beef roast whole into your stock pot, and fill the pot with enough water to cover the meat. Bring water to a boil then turn down to a simmer. Let it cook at a simmer for about 2 1/2 hours.
Cut two heads of cabbage into about eight chunks each and remove the core. Add the cabbage pieces to the pot with the corned beef. Cook for another 1/2 hour, and remove the pot from the heat.
Use cooking tongs and the large chef's knife to remove the corned beef from the water to a large bowl or surface. Use the slotted spoon to remove the cabbage from the water and place it in a bowl for storage. Allow the beef to cool enough to handle it, then wrap it in foil and store it in the refrigerator whole until you're ready to re-heat it. Refrigerate the cabbage.
To re-heat the beef, first unwrap it and move it to a large cutting surface. Trim all the fat from the meat and slice the meat directly against the grain. Thinner slices are better if you plan to make sandwiches, but if you're planning on a plate of corned beef and cabbage, make slices 1/4 to 1/2 inch thick.
Place the sliced corned beef into a large roasting pan, making sure not to have more than three or four slices depth in the pan. Add about 1/2 inch of water to the pan, cover it with foil and heat the meat at about 275 degrees Fahrenheit for 25 to 30 minutes. Add the cabbage in a layer at that point, and allow it to roast, covered, for about 15 more minutes. You should end with a tender and tasty corned beef and cabbage meal.