Preheat oven to 325°F.
Combine the flavor packet with other dried ingredients.
Rinse corned beef brisket well with cold water, then pat dry.
Rinsing will not change the flavor of the meat since the whole piece has been brined.
Trim the fat cap of the meat.
Sprinkle with seasoning mix and pat into the brisket
Put some sort of grate in the bottom of the roasting pan.
Place the meat on top of the grate fat side up.
Fill the bottom of the roasting pan with water, leaving room at the bottom of the grate (directly under the brisket).
Cover the pan with aluminum foil for two-thirds of the baking time.
Bake for 2 hours. Approximate baking time is 1.2 hours per pound
After 2 hours, remove from oven and remove the foil.
Add carrots and onions around the beef. if desired and continue baking.
Re-Wrap the brisket with aluminum foil, sealing it for the remainder of the time, an additional 1.5 -2 hours, depending on the size.
Feel free to check and make sure there is moisture in the foil, re-wrap and continue baking. It may take longer depending on desired level of tenderness.
Check for tenderness. Continue baking until the brisket is fork tender. It may take additional time depending on the thickness of the brisket.
Check the brisket by inserting a fork in the meat. If it goes in easily, it’s ready; if it meets with resistance, bake for another 30 minutes. If the brisket is tough, it hasn't cooked long enough!
Once the brisket is fork-tender, remove it from the oven and let it rest before slicing, covered loosely in foil.
Cut against the grain
To serve: Slice the rested beef on a cutting board (it should be very, very tender and almost falling apart
Serve with horseradish, carrots, onions, colcannon (potato/cabbage mixture) and Irish Soda bread.