Cooking corned beef is not difficult or complicated, but the debate between cooks over whether to cook corned beef fat side up or fat side down often gets as contentious as the tussle between St. Patrick and the snakes. Corned beef brisket is not a delicate meat, so almost any method of cooking will give you a tender and juicy result. The best way to decide how to cook yours is to go by the cooking method. Briskets cooked in liquid should be fat side up and those cooked directly on the heat source should be fat side down.
Fat Side Up
Coat the bottom of a heavy pot with a thin layer of olive oil. Not too much, just enough to keep things from sticking.
Turn the heat to medium-high and add sliced onions. One small onion per every 2 lbs. of corned beef is a good rule of thumb.
Place the corned beef on top of the onions, fat side up. The corned beef must fit entirely inside of the pot. Sprinkle on the corned beef seasoning that usually comes in a little packet with the beef.
Pour enough beer into the pot to come halfway up the side of the corned beef. Add enough water to come right up to the fat layer, but not cover it.
Bring the pot to a boil, then cover it and turn the beef down to a simmer. Cook the corned beef for approximately one hour per pound.
Insert an instant-read thermometer into the center of the corned beef. It is safely done when the internal temperature reaches at least 160 degrees Fahrenheit and the meat is uniformly light pink and completely opaque throughout.
Fat Side Down
Preheat your grill to medium-high or prepare the charcoals in your barbecue.
Spray a shallow pan with nonstick cooking spray.
Place the brisket, fat side down, in the oiled pan and tent it securely with aluminum foil.
Place the pan on the hot grill and cook the brisket for one hour per every pound of meat or until an instant read thermometer inserted into the center of the brisket reads at least 160 degrees Fahrenheit.