In an 8-quart pot, place the corned beef fat side up.
Add the Guinness and the corned beef seasoning packet, and add water until it covers the meat by 1 inch, approximately 8 cups.
Add the brown sugar and the bay leaves.
Cover and simmer over low heat for 4 to 5 hours or until the meat is tender and has an internal temperature of 160 F.
Right after I start simmering the corned beef, I rinse the carrots, wash the potatoes, and remove the outer leaves from the cabbage. Then remove the stem, cut the cabbage into quarters, and cut the potatoes in half.
Then I put the vegetables back into the refrigerator, taking them out 1 hour before use to bring them to room temperature.
When the meat reaches 160 F, remove it from the pot and place it on a foil-covered platter to keep it warm.
Add the potatoes and carrots to the same pot, cover, and simmer for 20 - 30 minutes or until they just soften.
Then add the cabbage wedges, cover, and continue cooking for another 15 minutes, until all the vegetables are tender but not mushy.
Add the corned beef back to the pot until it is warm.
Remove the corned beef from the pot and place it on a cutting board. Slice it against the grain into thin slices.
Arrange the meat and vegetables on a serving platter or serve directly onto plates.
Serve hot with spicy mustard or horseradish.