Start with a flat-cut corned beef brisket that comes with a spice packet.

1. Set aside the spice packet, and place the corned beef brisket in a very large pot of water, and boil for one hour.

2. After boiling for one hour, replace the water with fresh water, and add the contents of the spice packet.

3. Continue boiling in the fresh water for 2-3 more hours, until it's tender and a fork slips out of it easily.

4. Remove brisket from the pot, and soak it in very cold water, until it's fully cooled.

5. Trim the fat off, and slice the brisket into thin slices (about 3/16") PERPENDICULAR to the grain.

6. Arrange the slices in a glass pan covered with foil, and refrigerate until your party.

7. When you are ready to serve the corned beef, pour some of the reserved water from the second boiling over the beef. Cover tightly, and heat in the oven until warm.

8. Best served as sandwiches with rye bread, grey poupon, and swiss cheese (optional).

Useful information:
Corned beef water foams up a lot when you are boiling it. So, if you don't use a large enough pot, it will boil over.
You may want to save the water from the second boiling, to cook potatoes or cabbage in later, or to pour over the corned beef to keep it hydrated when you re-heat it for a party.
If you don't slice perpendicular to the grain, it will be very stringy and awful. This is very important.
Sometimes, a brisket might have parts with grain running in different directions. Separate the brisket into unidirectional sections before slicing it.
Corned beef will lose a lot of it's weight after it's cooked and the fat is trimmed off. Be sure to cook more than you need.
The corned beef will still have a red color even after you cook it. This is perfectly normal. The nitrites used in the curing process react with the myoglobin (the red pigment in meat), and keep it from turning brown.