For an extra layer of flavor, heat a little oil in a skillet over medium-high heat. Season the roast with salt and pepper and sear it on all sides until golden brown (about 3-4 minutes per side). Transfer the roast to the slow cooker.

In the same skillet, add the sliced onions and cook over medium heat until they are soft and caramelized (about 10-15 minutes). Stir them into the slow cooker over the roast.

In a bowl, mix the beef broth, Worcestershire sauce, garlic, thyme, and some more salt and pepper. Pour this mixture over the roast and onions in the slow cooker.

Cover the slow cooker and set it to low for 8 hours, or high for 4 hours. You want the roast to be tender enough to shred with a fork.

Once cooked, remove the roast and let it rest for a few minutes before slicing or shredding. Garnish with fresh parsley if desired, and serve with the onion gravy spooned over the top.