In a Dutch oven or other large heavy bottomed pot, add the brisket- placing in the center with the fat side down.
Sprinkle the seasoning packet out over the meat.
Slowly pour the beers in until both have been added. Add water to the pot to cover the beef.
Bring the mixture to a boil, then quickly reduce the temperature. Cover the pot and let the corned beef simmer for roughly 4 hours.
Thirty minutes before the corned beef is due to be done, carefully add the whole red potatoes.
15 minutes before the meal should be done, carefully add in the cabbage wedges & the carrots (if using). Use a spatula to push them under the broth. Add extra water if necessary.
Remove the brisket to a serving platter. Tent it with foil, and allow it to rest for 15 minutes, before slicing & serving.
While the brisket rests, use a slotted spoon to transfer all the vegetables to a waiting casserole dish. Spoon as much or as little of the broth in with them, and then cover the dish.
Make sure to slice the brisket against the grain, and serve it with the veggies.