Step 1

Sprinkle the brisket with 2 teaspoons salt, wrap it well, and refrigerate it overnight. This is more important than you think!

Step 2

The next day, preheat the oven to 350 degrees.

Step 3

In a very large (13-inch) Dutch oven, such as Le Creuset, heat the oil over medium-high heat. The pot should be large enough for the brisket to lie flat. Sprinkle 1 tablespoon salt and 1 teaspoon pepper all over the brisket. Sprinkle the Wondra flour all over and dust off the excess. Brown the brisket in the oil for 5 minutes on each side, adding more oil if necessary. Transfer to a large (18 × 14 × 2-inch) roasting pan and set aside.

Step 4

Put the yellow onions, red onions, and leeks in the Dutch oven, adding a few tablespoons of oil if the pot is dry, and sauté over medium to medium-high heat for 15 minutes, scraping up any brown bits, until the onions are tender and begin to brown. Add the garlic and cook for 2 minutes. Add the wine, beef stock, and thyme and cook for 3 minutes, scraping up any brown bits.

Step 5

Spoon half the onion and leek mixture under the brisket. Spread the tomato paste evenly on top of the brisket. Spoon the rest of the onions and leeks on top of the brisket, covering the tomato paste. Wrap the roasting pan tightly with heavy-duty aluminum foil. Roast for about 3½ hours, until the meat is extremely tender when tested with a meat fork.

Step 6

Discard the thyme bundle and allow the meat to rest at room temperature for 15 minutes before slicing thickly across the grain. Serve the meat with the warm onion mixture spooned on top. Sprinkle with salt and serve hot.