Place the cubed beef sirloin into the basin of a slow cooker.
In a small mixing bowl, whisk together the beef broth, Worcestershire sauce, minced garlic, salt, pepper, onion powder, and dried thyme.
Pour the liquid seasoning mixture over the steak bites and toss with a spoon to ensure even coating.
Distribute the cubed butter evenly across the top of the seasoned beef.
Secure the lid and cook on the LOW setting for 4 to 5 hours, or on the HIGH setting for 2 to 3 hours, until the beef is tender.
Garnish with fresh chopped parsley and serve immediately.