[The DIY corning part was removed.]

Sous-Vide Cooking: The day before serving, remove beef from the bag and rinse off all spices under cold, running water. Pat dry with paper towels. Re-seal in a vacuum bag and cook at 180°F until tender, about 10 hours. Proceed to step 4.

To Cook in a Dutch Oven: The day before serving, remove beef from the bag and rinse off all spices under cold, running water. Pat dry with paper towels. Preheat oven to 200°F. Place brisket in large Dutch oven, cover with water by several inches, and bring to a simmer over high heat. Remove from heat, cover with lid slightly ajar, place in oven, and cook until completely tender, about 10 hours.

Once beef is cooked, transfer to an airtight container along with cooking liquid. Let rest in refrigerator at least overnight, and up to 3 days.

The day of: Transfer cooking liquid to a large saucepan or Dutch oven along with carrots, potatoes, and cabbage. Top up with water until vegetables are submerged. Slice beef thinly against the grain and fan slices out in large skillet. Add 1 cup of liquid from pot to skillet and place skillet on top of pot. Cover skillet. Bring the pot to a boil over high heat, then reduce to a simmer. Cook until vegetables are completely tender and beef is heated through, about 45 minutes. Serve immediately with hot mustard.

Another from: https://sousvideways.com/sous-vide-corned-beef/ Through loads of experimentation, we've found that cooking the corned beef at 180F for 10 hours is the perfect combo. Leaving the beef in for 10 hours breaks down the connective tissue (collagen), which results in an extremely tender meat. Also, cooking the corned beef at a temperature of 180F is the sweet spot for that perfect, sliceable texture.