Pat the chuck roast dry with paper towels and season all sides generously with salt and pepper. Let it sit at room temperature for 30-45 minutes.
Preheat the oven to 325°F. Heat oil in a Dutch oven over medium-high heat and sear the roast on all sides until deeply browned, 3-4 minutes per side. Remove and set aside.
Add the sliced onion to the pot and cook for 3-4 minutes until softened. Add the garlic and cook for 30 seconds.
Pour in the beef broth and scrape the bottom of the pot to release the browned bits.
Return the roast to the pot along with the herb sprigs. Cover tightly with a lid or two layers of sealed foil.
Braise in the oven for 3-4 hours, adding the potatoes and carrots either at the start or with 60-90 minutes of cook time remaining.
Check for doneness with a thermometer (195-205°F internally) or the fork test. Return to the oven in 20-30 minute increments if needed.
Remove the roast and vegetables and set aside, covered. For gravy, whisk the cornstarch and cold water into the strained pan liquid and simmer for 2-3 minutes until thickened.
Serve the roast with the vegetables and gravy.