Start by patting your 14-pound chuck roast dry with paper towels. Season generously with salt and black pepper on all sides.
In a large Dutch oven, heat 2 tablespoons of vegetable oil over medium-high heat. Carefully place the seasoned roast into the pot. Sear on all sides for about 4-5 minutes until it develops a beautiful brown crust.
Once browned, remove the roast from the pot and set it aside. In the same pot, add 1 cup of sliced onion and 1 teaspoon of minced garlic. Sauté for about 3-4 minutes until the onions become translucent.
Stir in 14 ounces of diced tomatoes, 2 bay leaves, 3/4 cup of brown sugar, 1 teaspoon of salt, and 1/2 teaspoon of black pepper. Mix well to combine.
Place the seared roast back into the pot, then add the 4 ounces of mushrooms on top.
Cover the Dutch oven and reduce the heat to low. Allow the roast to simmer gently for about 3 hours.
After 3 hours, check for doneness using a meat thermometer. The internal temperature should reach at least 190°F.
Once done, remove the roast and let it rest for 10-15 minutes before slicing. Serve with the rich gravy and vegetables.