In a Dutch oven or heavy pot, heat oil over medium-high heat. Season the roast with salt and pepper on all sides. Sear until browned on all sides, about 4-5 minutes per side. Remove from the pot and set aside.
Reduce the heat to medium. Add the chopped onions, carrots, and celery. Sauté for about 5-7 minutes, until the vegetables begin to soften.
Add garlic and cook for 1 minute. Stir in tomato paste and cook an additional minute. Season with salt and pepper.
Stir in beef stock, red wine (or additional beef stock), Worcestershire sauce, and Dijon mustard. Scrape up any browned bits from the bottom of the pot.
Place the roast back into the pot, making sure it's submerged in the liquid. Top with thyme, rosemary, and bay leaves.
Bring the mixture to a gentle simmer. Cover and braise for 3-4 hours, or until the meat is fork-tender.
Transfer the roast from the pot to plate. Return the mixture to a boil. In a bowl, mix cornstarch with 2 tablespoons water. Stir it into the pot, lower the heat, and simmer 3-4 minutes. Adjust seasoning as needed.
Add the beef back to the pan whole or in large chunks. Serve over mashed potatoes, noodles, or rice.