Step 1

Heat the oil in a large, deep sauté pan or cast iron skillet over medium heat until shimmering. Add the onions and cook on medium-low to medium heat, stirring frequently, until the onions have caramelized lightly, about 20 minutes. Meanwhile, sear the brisket.

Step 2

Pat the brisket dry with paper towels. Season generously all over with salt and pepper. Heat a large skillet or sauté pan over medium-high heat and turn on your vent or fan, if you have one. Add the brisket and sear, flipping once, until a golden-brown crust forms. Transfer to a 6-quart or larger slow cooker fat side up. Sprinkle the minced garlic over the brisket.

Step 3

When the onions are ready, pile them on top and around the meat. Mix the broth, Worcestershire sauce, and soy sauce or tamari together and pour into the slow cooker.

Step 4

Cover and cook until the brisket is very tender, 6 to 8 hours on the LOW setting. Switch to the WARM setting and let rest for at least 20 minutes. (If your slow cooker doesn't have a WARM setting, transfer to a baking dish and cover tightly with aluminum foil while resting.)

Step 5

The brisket can be sliced or shredded immediately and served with the onions and juices. Or, let the meat cool, then refrigerate overnight. Before reheating, scrape away and discard the layer of fat that has formed around the meat.

Step 6

To reheat: Heat the oven to 300°F. Transfer the brisket and all its juices to a baking dish and cover tightly with a lid or two layers of aluminum foil. Heat in the oven for 1 hour or until warmed through (time will depend greatly on the size and shape of the brisket; cut into smaller pieces for faster reheating).