Preheat your Dutch oven over medium-high heat. Pat the chuck roast dry with paper towels and season both sides with salt and pepper. Add olive oil to the pot and sear the roast on all sides until nicely browned, about 3-4 minutes per side. This step locks in flavor and gives the meat a beautiful crust.
Transfer the roast to a plate and reduce heat to medium. Add more olive oil if needed and toss in the sliced onions. Cook slowly for 15–20 minutes, stirring often, until the onions are golden, soft, and caramelized. Don’t rush this step—it’s key to that classic French onion flavor.
Add garlic to the onions and sauté for another minute. Stir in the tomato paste, Worcestershire sauce, balsamic vinegar, and thyme. Cook for 2–3 minutes until everything is well mixed and fragrant.
Pour in the white wine (or extra broth) and scrape up any browned bits from the bottom of the pot. Let the wine simmer for 2 minutes. Then add the beef broth and stir everything together.
Return the seared roast to the pot, nestling it into the onions and liquid. Cover with a lid and transfer to a preheated oven at 300°F (150°C). Roast for 3 hours, or until the beef is fall-apart tender.
If you’d like a thicker sauce, remove the beef once cooked and whisk in 2 tablespoons of flour to the broth. Simmer on the stove for 5–10 minutes until thickened, then return the beef and ladle the sauce on top.