Brown the brisket on both sides under the broiler or in a skillet.

Place a large sheet of foil in a roasting pan.

Place the brisket on the foil.

Arrange sliced onions on top of the brisket.

In a bowl, mix together brown sugar, red wine vinegar, ketchup, water, minced garlic, salt, and pepper.

Pour the sauce mixture over the brisket and onions.

Seal the foil tightly around the brisket, ensuring no juice can leak out.

Cook at 350 degrees Fahrenheit for 2-3 hours, depending on the size of the brisket.

Remove from the oven and let cool.

Carefully remove the brisket from the pan and slice it.

Return the sliced brisket to the pan with the sauce.

Continue cooking for another 1-2 hours until very tender.

For best flavor, refrigerate overnight and serve the next day.