In a small mixing bowl, combine the 1 tbsp kosher salt, 1 tsp black pepper coarsely ground, 1 tsp garlic powder, 1 tsp onion powder, 1 tsp smoked paprika, and ½ tsp dried thyme. Mix well. Pat the 4 lb beef brisket flat cut completely dry with paper towels, then rub the spice mixture all over every surface of the meat. For best results, do this the night before and refrigerate uncovered — but even 30 minutes at room temperature makes a difference.

Preheat your oven to 325°F. Heat the 2 tbsp vegetable oil in a large Dutch oven or heavy oven-safe pot over medium-high heat until shimmering. Sear the 4 lb beef brisket flat cut fat-side down first for 4–5 minutes until deep golden brown, then flip and sear the other side for another 3–4 minutes. Sear the edges briefly as well. Remove the 4 lb beef brisket flat cut and set aside on a plate.

Reduce the heat to medium. Add the sliced yellow onions thinly sliced to the same pot and cook, stirring occasionally, for 8–10 minutes until softened and beginning to turn golden. Scrape up any browned bits from the bottom of the pot as the 2 yellow onions thinly sliced release their moisture.

Add the minced cloves garlic minced, 2 stalks celery roughly chopped, and 2 carrots roughly chopped. Cook for 2 minutes, stirring frequently. Add the 2 tbsp tomato paste and stir it into the vegetables, cooking for another 1–2 minutes until it darkens slightly and becomes fragrant.

Pour in the 1 cup dry red wine such as Cabernet Sauvignon and let it simmer for 2–3 minutes, scraping up all the browned bits from the bottom of the pot. This deglazing step is key to a rich, complex braising liquid.

Stir in the 1 can crushed tomatoes, 2 cups beef broth low sodium, and 1 tbsp Worcestershire sauce. Nestle the 4 lb beef brisket flat cut back into the pot fat-side up — the fat will baste the meat as it braises. Tuck in the 2 whole bay leaves and ½ tsp dried thyme around the meat. The liquid should come about halfway up the sides of the beef brisket flat cut; add a splash more 2 cups beef broth low sodium if needed.

Bring the liquid to a gentle simmer on the stovetop, then cover the pot tightly with a lid (or two layers of aluminum foil if your lid isn't snug) and transfer to the preheated oven. Braise for 3 to 3.5 hours, until the 4 lb beef brisket flat cut is completely fork-tender and a knife slides in with no resistance. Check once at the 2-hour mark to make sure there's still plenty of liquid; add a little 2 cups beef broth low sodium if it looks dry.

Remove the pot from the oven. Carefully transfer the 4 lb beef brisket flat cut to a cutting board and tent loosely with aluminum foil. Let it rest for at least 15–20 minutes. Meanwhile, discard the 2 whole bay leaves and ½ tsp dried thyme. Skim any excess fat from the surface of the braising liquid. Taste the sauce and adjust seasoning with 1 tbsp kosher salt and 1 tsp black pepper coarsely ground as needed. If you'd like a thicker sauce, simmer it on the stovetop over medium heat for 5–10 minutes.

Slice the 4 lb beef brisket flat cut against the grain into 1/4-inch thick slices. This is essential — cutting with the grain will result in tough, chewy meat. Arrange slices on a platter or return them to the pot with the braising sauce. Spoon plenty of sauce and vegetables over the top, garnish with fresh fresh flat-leaf parsley roughly chopped, and serve.