Preheat the oven to 350°F.
Heat 2 tablespoons of the oil over medium- high heat in a heavy pot (such as cast iron or a Dutch oven) large enough to hold the brisket.
Add the brisket and brown on both sides, 5 to 7 minutes per side.
Transfer the brisket to a platter and pour away the excess fat from the pot.
Combine the remaining 3 tablespoons of oil with the garlic in a small bowl, and when brisket is cool enough to touch, rub the garlic mixture over the brisket, top and bottom.
Put half of the onions in the bottom of the pot and place the brisket on top.
Combine all the remaining ingredients, except the remaining onions and the stock, in a medium bowl. Mix well and spoon over the top of the brisket, then top with the onions.
Pour the stock around the outside of brisket, cover with a lid or very tightly with foil, and bake for 4 to 5 hours, until fork- tender (start checking after about 3 ½ hours). Oh, and don’t be shocked by how much it shrinks.
Transfer to a cutting board, cover loosely with foil, and let rest for about 20 minutes before slicing.
Slice across the grain to serve— always across the grain (this is true for any protein), as that will shorten up the fibers and make it more tender to eat.
Excerpted from Sam the Cooking Guy: Recipes with Intentional Leftovers. Copyright 2020 by Sam Zien. Photography by Lucas Barbieri. Reproduced by permission of The Countryman Press, a Division of W.W. Norton & Company. All rights reserved.