2 tablespoons finely chopped parsley
For the meatballs: In a large mixing bowl, combine everything from ground beef to salt. Mix well so that all ingredients are combined evenly. Roll into meatballs, 1 inch in diameter.
Optional: Place rolled meatballs on a baking sheet lined with parchment paper. Freeze for 1 hour.

In a 6-quart slow cooker, whisk flour and melted butter until it becomes a paste. Gradually whisk in beef broth. Mix in mushrooms, onions, garlic and Worcestershire sauce.
Gently add meatballs.
Cook on high for 4 hours, or on low for 6 hours.
Stir in sour cream and parsley.
Serve as is or over rice or pasta.