Season the beef with 1 teaspoon salt and ¼ teaspoon pepper and place in the bottom of a slow cooker. Add the onion, potatoes, and carrots.
Stir the tomato paste, coffee, Worcestershire sauce, and brown sugar together and pour it over the beef and vegetables. Stir things around just a little. Cover and cook on low until the beef and vegetables are tender, 8 to 10 hours.
Slice the beef and serve with the vegetables and sauce, sprinkled with the parsley.