Rinse the corned beef if desired, then place it in a large Dutch oven or heavy pot with the spice packet, onion, garlic, bay leaf, and enough water to cover.
Bring to a boil, reduce to a gentle simmer, cover, and cook for about 2 hours 30 minutes to 3 hours until the beef is getting tender.
Check the thickest part with a thermometer and continue cooking until the corned beef reaches about 195 to 203°F for tender slices.
Add the potatoes and carrots, then simmer for about 15 minutes.
Add the cabbage wedges and cook another 15 to 20 minutes until all vegetables are tender.
Remove the corned beef and let it rest for 15 minutes before slicing across the grain.
Serve the sliced corned beef with the vegetables and some of the cooking broth, plus mustard if desired.