Season chuck roast with salt & pepper. Set aside.
Add the butter and thinly sliced onions to a pot. Cook them low & slow until golden and caramelized. This is the step that makes the entire dish. Be patient! About 20-25 mins. Add the garlic in the last minute.
Stir in the tomato paste, worcestershire, balsamic, thyme, and beef broth. Stir.
Add the roast back in. Nestle it into the onions. Pour in the bone broth, cover, and cook at 350F for 3-3.5 hours until it shreds easily.
Remove, shred using two forks and stir so the onions and broth coat the meat. Taste and adjust salt. Pop it back in the oven at 400F for 30 mins.
Remove, shred the cheese on top and broil 2 mins until bubbly and golden, and top with fresh parsley.
