Season the chuck roast generously with salt and black pepper.
Heat olive oil in a large Dutch oven over medium-high heat. Sear the roast on all sides until deeply browned. Remove and set aside.
Reduce heat to medium. Add sliced onions and cook slowly until caramelized and golden, about 25–30 minutes.
Stir in garlic and cook for 30 seconds until fragrant.
Pour in beef broth and Worcestershire sauce, scraping up any browned bits.
Add thyme and bay leaf, then return the roast to the pot.
Cover and cook in a preheated 325°F (165°C) oven for 3 hours, or until fork-tender.
Remove the roast and let rest. If desired, thicken sauce with cornstarch slurry.
Slice or shred beef and serve with onions and sauce.