Preheat the Oven: Set the oven to 350°F (175°C).
Season the Brisket: Generously season the brisket on all sides with kosher salt and black pepper.
Brown the Brisket: Heat a small amount of oil in a large ovenproof pot over medium-high heat. Once hot, place the brisket in the pot and brown on all sides, about 10 minutes total. Use tongs to turn the brisket for even browning. Remove from pot and set aside.
Build the Braising Base: In the same pot, add the onions, garlic, thyme, bay leaves, whole peeled tomatoes, tomato paste, and red wine. Stir well to combine and season lightly with salt and pepper.
Begin Braising the Brisket: Place the browned brisket back in the pot, fat side up, resting it on top of the mixture. Cover the pot with a lid (or aluminum foil) and transfer to the preheated oven.
Braise the Brisket: Cook the brisket for 3.5 hours. Every 30 minutes, use a ladle or spoon to baste the brisket with the juices in the pot.
Prepare the Sauce: Once the brisket is tender, remove it from the pot and let it rest on a cutting board for 10–15 minutes. Use an immersion blender directly in the pot to blend the sauce until smooth and silky. If using a regular blender, let the mixture cool slightly, then blend in batches and return to the pot to reheat.
Slice and Serve: Slice the rested brisket against the grain into even slices. Serve over the braised onions and tomatoes, generously spooning the sauce on top. Garnish with fresh parsley before serving.