01 - Rinse the corned beef brisket under cold water to remove excess brine. Place it in a large stockpot.
02 - Add water to cover the brisket by at least 1 inch (about 12 cups). Add the spice packet, bay leaves, peppercorns, mustard seeds (if using), onions, and garlic.
03 - Bring to a boil over high heat. Skim off any foam, then reduce heat to low. Cover and simmer for 2 hours.
04 - Add the potatoes and carrots to the pot. Simmer, covered, for 20 minutes.
05 - Add cabbage wedges, nestling them into the broth. Simmer for another 20–25 minutes, until vegetables and brisket are tender.
06 - Remove the brisket to a cutting board. Let rest for 10 minutes, then slice against the grain.
07 - Arrange sliced brisket and vegetables on a large platter. Ladle some of the cooking liquid over the top. Season with salt and pepper as needed. Serve hot.