Preheat your oven to 250 degrees Fahrenheit. Peel and quarter the potatoes. Peel and chop the onions. Peel and slice the carrots into inch-thick pieces. Strip thyme leaves from the stems.
Trim excess fat from the chuck roast, cutting off any large pieces.
In a bowl, mix salt, pepper, and a generous amount of chili powder. Rub the spice mixture over the chuck roast, ensuring an even coating.
In a large skillet, melt butter over medium heat. Add onions, celery, and carrots. Sauté until slightly softened.
Heat a large skillet over medium-high heat. Add a bit of olive oil, then sear the chuck roast on all sides until browned. Place the chuck roast in a roasting pan or Dutch oven. Sprinkle thyme over the roast and vegetables. Pour beef broth over the roast and vegetables.
Cover the roasting pan or Dutch oven and place it in the preheated oven. Roast for 5 hours, or until the chuck roast is tender and shreds easily. Once cooked, remove the chuck roast and vegetables from the pan.
Strain the liquid from the pan into a saucepan. In a separate bowl, mix cornstarch with cold water to create a slurry. Add the slurry to the strained liquid and bring it to a simmer, stirring constantly until thickened.
Shred the chuck roast using two forks. Add the shredded meat back into the thickened gravy, mixing well. Plate the pot roast with a generous helping of vegetables. Enjoy!