1 piece (5 pounds) untrimmed flat-cut brisket.
1 tablespoon kosher salt, plus more to taste.
1 2 teaspoons freshly ground black pepper, plus more to taste.
3 tablespoons vegetable oil.
3 medium yellow onions, thinly sliced.
4 rib celery, cut into 2-inch pieces, coarsely chopped leaves.
6 garlic cloves, mashed.
2 glasses of red wine (such as Merlot or Pinot Noir).
1 can (28 ounces) chopped tomatoes.
1 2 cups tomato paste.
2 tablespoons brown sugar.
1 2 bunches of fresh thyme.
2 bay leaves.
4 medium carrots, cut in half lengthwise and diagonally into 2-inch pieces.
Preheat oven to 325°F.
Brown the brisket:
Season the brisket with most of the salt and pepper. Heat the oil in a large oven pan or Dutch oven over medium-high heat.
Cook the brisket, turning occasionally, until browned on all sides, 10 to 12 minutes. Transfer to a plate.
Cook the vegetables: Put the onion, celery, and garlic in the pan and stir in the remaining fat. Season with the remaining salt and pepper. Cook, stirring occasionally, until onions are soft and translucent, about 5 minutes.
Add the liquid and aromatics and simmer: add the wine, crushed tomatoes, tomato paste, brown sugar, thyme and bay leaves, stir to combine.
Place the brisket in the liquid with the fat side up. Cover the pan and simmer in the oven until the meat is tender, about 3 hours.
Add the carrots: Remove the lid and snuggle the carrots around the brisket. Cook uncovered until the carrots are tender (not soft) and the brisket is brown and crispy on top, taking 35 to 45 minutes.
Slice the brisket into thin slices to make the sauce: Remove the brisket from the pan, cut into thin slices and serve. Place on a deep dish.
In the meantime, skim off the fat from the surface of the stew with a spoon and discard. Heat over medium-high heat and cook until the liquid thickens to a sauce-like consistency, 5 to 10 minutes. Remove the thyme sprigs and bay leaves. Season and season with salt and pepper as desired.
Pour the sauce over the brisket and serve.