Preheat your oven to 325 degrees F and prepare a large roasting pan.

Rinse the corned beef brisket under cold water and pat dry with paper towels. Place in the roasting pan.

In a small bowl, mix together whole grain mustard, brown sugar, and cracked black pepper. Rub this mixture over the top of the brisket, especially the fatty side.

Sprinkle the spice packet contents evenly over the bottom of the roasting pan.

Pour 4 cups of water carefully into the pan without washing off the mustard from the brisket.

Cover the pan tightly with foil and bake for 2 hours.

While the beef is cooking, prepare the vegetables by cutting the cabbage into halves, removing the core, and slicing into wedges. Peel and cut the onion into wedges, trim, peel, and chop the carrots into 2-3 inch pieces.

After 2 hours, remove the corned beef from the oven and increase the temperature to 350 degrees F.

Add the garlic cloves to the roasting pan juices. Arrange the cabbage, onion, carrots, and potatoes around the brisket, spooning some pan juices over the vegetables.

Return the pan to the oven and bake covered for 30 minutes.

After 30 minutes, spoon more broth over the veggies and bake uncovered for an additional 30 to 45 minutes until the carrots and potatoes are fork-tender.

Slice the corned beef into thin strips using a serrated knife and arrange on a platter with the vegetables. Serve warm.