Season trimmed brisket with kosher salt, ground pepper and celery salt, pressing to adhere on all sides. Wrap tightly in plastic wrap and refrigerate on a baking tray (to catch any drips) 3 hours, or best overnight.
Bring brisket to room temperature. Place a rack in lower third of oven and preheat to 275°F.
On the stove top heat bacon fat on High in a large roasting pan set over 2 burners. Sear brisket on all sides until browned, 7–10 minutes. Transfer to a platter to rest.
Reduce heat to medium and add the vegetables to pan. Cook until browned and just soft, about 15 minutes. Add the wine or juice, bring to a boil, and cook until almost evaporated, 10 minutes. Add the garlic, thyme and bay leaves. Pour broth to come halfway up side of pan, and bring to a boil. Using a spoon or spatula, move vegetables to the sides of the pan and place the seared brisket in center. Cover tightly with foil. Braise in oven until meat is tender, 3 to 3.5 hours. You're looking for fork tender brisket.
Transfer brisket to a tray, cover with foil and keep warm. Remove and discard the fat from surface of braising liquid (optional). Strain braising liquid into large measuring cup and transfer cooked vegetables to serving bowl. Cover to keep warm. Cook braising liquid over high heat until reduced by half, about 15 minutes (or thicken with 2 tablespoons cornstarch and 1/4 cup water mixed).
Transfer brisket to a cutting board and slice against the grain. Arrange on platter and pour reduced braising liquid over and serve immediately with vegetables.
Often times you can purchase an entire brisket that includes the flat and point (deckle). Sometimes the butcher just has one or the other. For this recipe I used a flat brisket, which is great for braising or making corned beef. I trimmed the 8 lb flat brisket of all excess fat and the weight was a total of 6.5 lbs.
If you do not drink red wine (alcohol), feel free to substitute Pomegranate juice or Concord grape juice (non-alcoholic). A friend told me it worked well.