Place vegetables (carrots, celery and onion) in bottom of the crockpot.
Place roast on top of vegetables.
In a small bowl combine Worcestershire sauce, garlic, pepper and parsley.
Pour the mixture over the roast.
Place butter slices on top.
Place lid on slow cooker and cook on low 8-9 hours.
Remove roast and veggies from slow cooker onto a platter.
Serve and enjoy!