Preheat & Season the Roast: Preheat oven to 300°F (150°C). Pat the chuck roast dry with paper towels, then season all over with 1 teaspoon kosher salt and 1 teaspoon black pepper.
Sear the Roast: In a large Dutch oven, heat 2 tablespoons olive oil over medium-high heat. Sear the chuck roast for 5-6 minutes on each side, until deeply browned. You can sear the edges of the roast if you’d like, but it’s not necessary. Remove the roast to a plate and set aside.
Sauté Aromatics: Reduce heat to medium. Add sliced onions and cook for 2-3 minutes, stirring occasionally. Add 4 cloves minced garlic and cook for another 30 seconds, until fragrant.
Deglaze: Pour in 1 cup red wine, scraping up any browned bits from the bottom of the pot. Simmer for 2 minutes, letting the alcohol cook off slightly.
Build the Braising Liquid: Stir in 2 tablespoons tomato paste, 2 teaspoons Dijon mustard, 2 teaspoons Worcestershire sauce, and 2 cups beef broth. Add 6-8 thyme sprigs and 2 bay leaves.
Return the seared roast to the pot, nestling it into the liquid. The liquid should cover the roast about ½-¾ of the way up. If it doesn’t, add more broth to the pan.
Slow Braise in the Oven: Cover the Dutch oven with an oven-safe lid and transfer to the preheated oven. Cook for 2 hours.
Add Vegetables (Halfway Through Cooking Time): Carefully remove the Dutch oven from the oven. Add 1 lb carrots, 3 ribs celery, and 1 ½ lb baby potatoes around the roast, ensuring they're submerged in the braising liquid.
Cover and return to the oven for another 1.5-2 hours, or until the roast is fork-tender and easily shreds with two forks.
Thicken the Gravy (Optional): Once the roast is done, remove it from the pot and set aside, leaving the cooking liquid in the dutch oven. Discard thyme sprigs and bay leaves. In a small bowl, whisk together 3 tablespoons cornstarch with 3 tablespoons cold water until smooth. Stir into the braising liquid over medium heat on the stovetop, cooking for 4-5 minutes until thickened.
Serve & Garnish: Slice or shred the roast, spoon the gravy over the top, and garnish with fresh parsley. Serve with the vegetables and enjoy!