• Remove the chuck roast from the refrigerator and let it sit at room temperature for about 30 minutes.
• Pat the roast thoroughly dry with paper towels, then season all over with kosher salt and black pepper.
• Preheat the oven to 300°F.
• Heat olive oil in a large Dutch oven or heavy pot with a tight-fitting lid over medium-high heat. Once hot, add the roast and sear for 3-4 minutes per side until a deep brown crust forms. Transfer the roast to a plate.
• Reduce heat to medium. Add the sliced onion to the pot and cook for 4-5 minutes, scraping up the browned bits from the bottom.
• Add the smashed garlic and cook for 30 seconds until fragrant.
• Pour in the beef broth and Worcestershire sauce, stirring well to combine. Add the fresh thyme sprigs, if using.
• Return the roast to the pot along with any accumulated juices.
• Check the liquid level; it should come about halfway up the sides of the roast. Add a bit more beef stock if needed to reach that level.
• Cover with a tight-fitting lid and transfer to the oven. Cook for 3½-4 hours, flipping the roast once halfway through, until fork-tender and easily pulled apart.
• Remove the roast from the oven and let it rest, uncovered, for 10-15 minutes. Transfer the roast to a platter or cutting board and gently pull it apart with forks.

Gravy

• Strain the braising liquid from the pot into a bowl (discard solids). Skim off excess fat and return the pot to medium heat.
• Add butter and melt. Whisk in the flour and cook, stirring constantly, for 1-2 minutes until lightly golden and bubbly. Gradually whisk in the strained pan juices (start with 2 cups).
• Bring to a gentle simmer and cook 3-5 minutes, whisking often, until thickened to your desired consistency. Season with salt, pepper. Thin with extra broth if too thick.
• Serve the shredded roast warm with mashed potatoes and generous ladles of classic pan gravy.