Pat chuck roast completely dry with paper towels - wet meat won't brown properly. Season generously with salt and pepper on all sides, making sure to cover the entire surface.

Heat 2 tablespoons olive oil in a heavy pot or Dutch oven over high heat until smoking hot. Place the roast in the pot and sear without moving it for 4-5 minutes per side until a deep golden-brown crust forms. Don't skip this step - it's where the flavor foundation is built.

Remove the seared meat and set aside. Add 4 tablespoons butter to the same pot. Add the thickly sliced onions and reduce heat to medium-low. Cook, stirring occasionally, for 15-20 minutes until the onions turn deep golden brown and sweet. Let them sit long enough between stirs to actually caramelize - don't rush this step.

Pour in 1 cup red wine (or extra beef broth if not using wine). Use a wooden spoon to scrape up all the browned bits stuck to the bottom of the pot - this is pure flavor. Let the wine reduce by half, about 3-4 minutes.

Add 3 cups beef broth, 2 tablespoons Worcestershire sauce, 1 tablespoon balsamic vinegar, French onion soup mix (if using), and bay leaves. Stir everything together. The liquid should come about halfway up the sides of where the meat will sit - don't cover it completely.

Return the seared roast to the pot, nestling it into the onions and liquid. Cover tightly with a lid. Place in a preheated 300°F oven and cook for 3-4 hours, or until the meat is fork-tender and shreds easily. Check once halfway through - if the liquid is reducing too much, add a splash more broth.

Remove the pot from the oven. Transfer the roast to a cutting board and let it rest for 10 minutes. Skim any excess fat from the surface of the gravy if desired. Slice or shred the meat, return it to the pot with the onions and gravy, or serve it plated with gravy spooned over top. Optional: top with shredded Gruyere cheese and broil for 2-3 minutes until melted and bubbly.