Remove brisket from refrigerator 30–45 minutes before cooking to come toward room temperature. Pat dry with paper towels. Combine kosher salt, black pepper, smoked paprika, and garlic powder in a small bowl. Rub olive oil over the entire surface of the brisket, then evenly rub the dry spice blend all over, pressing gently so the rub adheres.

Sear (optional, for color)

Preheat a large skillet or your oven to 450°F (232°C) if using the oven-sear method. Heat 1 tablespoon olive oil or beef drippings in an oven-safe skillet over medium-high heat until shimmering. Sear brisket fat-side down 3–4 minutes until browned, then turn and sear the other side 3 minutes. Transfer brisket to the braising pan, fat-side up.

Caramelized Onion Au Jus

Caramelize onions

In the same skillet used for searing (reduce heat to medium-low), add 2 tablespoons butter and 1 tablespoon olive oil. Add the thinly sliced onions and sprinkle 1 teaspoon sugar over them. Cook, stirring every 2–3 minutes, at medium-low to medium heat for 20–28 minutes until the onions are deep golden and jammy. If they brown too quickly, lower the heat and add a tablespoon of water to prevent burning.

Add aromatics and tomato paste

Stir in the minced garlic and 1 tablespoon tomato paste; cook 1–2 minutes until fragrant and the tomato paste darkens slightly.

Deglaze and build au jus

Increase heat to medium-high and pour in 1 cup dry red wine (or 1 cup beef broth if not using wine) to deglaze the pan, scraping up browned bits from the bottom with a wooden spoon. Reduce the wine by half, about 3–5 minutes. Add 2 cups low-sodium beef broth, 1 teaspoon Worcestershire sauce, thyme sprigs, and bay leaf. Stir and bring to a gentle simmer. Taste and season with 1 teaspoon coarse kosher salt and 1/2 teaspoon freshly ground black pepper, adjusting to taste. Simmer 5 minutes to meld flavors, then remove thyme sprigs and bay leaf.

Strain (optional) and reserve

For a smoother au jus, strain the onion-broth mixture through a fine-mesh sieve into a bowl, pressing on solids to extract flavor. Return strained liquid to the braising pan to use for braising; reserve solids if you like extra caramelized onions for serving.

Braising and Finishing

Assemble for braising

Preheat oven to 300°F (150°C). Place the seasoned and seared brisket fat-side up in the braising pan. Pour the caramelized onion au jus (strained liquid) over the brisket until the liquid reaches about 1/3–1/2 up the side of the meat (approximately 1 to 1 1/2 cups). Add thyme sprigs and bay leaf to the pan if you removed them earlier. Dot any exposed areas with the remaining 1 tablespoon butter if desired for richer flavor.

Cover and braise

Cover the pan tightly with a lid or aluminum foil (double layer). Place in the preheated oven and braise until the brisket is fork-tender, about 2 to 2 1/2 hours for a 2–2.5 lb piece. Check at 90 minutes: if the liquid is evaporating too quickly, add up to 1/2 cup extra beef broth. The brisket is done when a fork slides easily into the meat with little resistance.

Rest and slice

Remove the brisket from the oven and transfer to a cutting board. Tent loosely with foil and rest 20–30 minutes to allow juices to redistribute. Strain the braising liquid into a saucepan and skim excess fat from the surface. If you reserved caramelized onion solids, stir them back into the au jus now. Keep warm.

Serve

Slice the brisket thinly against the grain into 1/8–1/4-inch slices. Arrange on a platter and spoon warm caramelized onion au jus over the slices, or serve the au jus on the side for dipping. Garnish with chopped fresh parsley if desired.