Fill a large pot with water (about 16 cups) then add the onion, garlic, parsley,thyme, beef and seasoning packet, bring to a simmer, cook on low for 2.5 to 3hours or until tender.
Remove the brisket from the broth, skim out the onion,garlic, celery and herbs, then add the carrots and potatoes and cook until tender, about 30 minutes, meanwhile, make the cabbage.
Ina large skillet, add the butter, once melted, add the cabbage (you might have to cover it and let it wilt before stirring it) saute until slightly tender adding about 1/2 cup or so (you might need more) of the cooking liquid from the corned beef to help it cook down.
Remove the fat cap from the beef (optional) slice the beef thinly against the grain,then serve with the carrots, potatoes, and sauteed cabbage
