Place the corned beef brisket in a large pot and cover it with water. Add the spice packet, black peppercorns, bay leaves, and mustard seeds.

Bring the water to a boil over high heat, then reduce the heat to low and cover the pot. Simmer for about 2 hours, or until the meat is tender.

After 2 hours, add the carrots and potatoes to the pot. Continue to simmer for an additional 30 minutes.

Finally, add the cabbage wedges to the pot and cook for another 15-20 minutes, or until the cabbage is tender.

Remove the corned beef from the pot and let it rest for 10 minutes before slicing against the grain.

Serve the sliced corned beef with the vegetables on the side. Drizzle with some of the cooking liquid if desired.