Pat the chuck roast dry, season with the 2 tsp salt and 1 tsp pepper, and sear in the 2 tbsp vegetable oil over medium-high heat in a Dutch oven for 4 to 5 minutes per side until deeply browned. Remove and set aside.

Reduce heat to medium and cook the quartered onion and 4 smashed garlic cloves in the drippings for about 3 minutes, until the onion edges are golden.

Add the carrots, potatoes, and celery to the pot. Pour in the undrained diced tomatoes, 1 cup beef broth, and 1 tbsp Worcestershire sauce. Add the 1 tsp thyme and 1 tsp rosemary. Return the roast to the pot on top of the vegetables, cover, and braise in a 325°F (165°C) oven for 3 to 3.5 hours, until the meat reaches 200 to 205°F (93 to 96°C) internally.

Remove the roast and vegetables. Pour the braising liquid into a saucepan and simmer over medium heat. Stir together the 2 tbsp cornstarch and 2 tbsp cold water, then whisk into the liquid and cook for 2 to 3 minutes until the gravy thickens.

Slice the roast across the grain into 1/2-inch pieces, arrange on a platter with the vegetables, and ladle the gravy over the top.