In a large bowl, mix together hamburger, soup mix, crumbs and egg. Shape into small meatballs. I use my tablespoon measuring spoon, it's the perfect size. You can either fry them in a skillet with a little oil or bake them at 350 for 15 min or until browned. Remove from pan and drain on paper towels.
In a small bowl, stir together sour cream and flour. Whisk in milk and mustard. Stir sour cream mixture into skillet. Cook and stir until thickened and bubbly. Add meatballs to sauce, cook and stir for 1 minute more. Serve over hot cooked noodles.