Preheat your oven to 325°F (165°C).
Pat the beef dry, season generously with salt and pepper, and sear in a hot, oven-safe pan or Dutch oven until browned on all sides.
In a bowl, whisk together the balsamic vinegar, brown sugar/honey, soy sauce, Worcestershire sauce, Dijon mustard, and thyme.
Place the onion and garlic around the beef.
Pour the balsamic mixture and beef broth over the meat.
Cover tightly with a lid or heavy-duty foil.
Roast in the oven for 3–4 hours, basting the beef with the pan juices every hour, until it is fork-tender and pulls apart easily.
Remove the lid for the final 20–30 minutes of cooking.
If the sauce hasn’t thickened into a sticky syrup, remove the beef, place the pan over high heat on the stove, and reduce the remaining liquid until it coats the back of a spoon.
Shred the beef slightly or serve in large, tender chunks, drizzled with the thickened balsamic glaze.
