Prepare the Sauce – Spray the slow cooker with nonstick spray. Add the dry onion soup mix, beef broth, cream of mushroom soup, and minced garlic. Whisk to combine.
Add Meatballs and Mushrooms – Stir in frozen meatballs and sliced mushrooms until well coated in the sauce.
Slow Cook – Cover and cook on LOW for 4-6 hours or HIGH for 2-3 hours until meatballs are heated through.
Stir in Sour Cream – Once the cook time is complete, stir in the sour cream for a smooth, creamy texture.
Cook the Noodles – In the meantime, cook and drain the egg noodles according to package instructions.
Combine & Serve – Add the cooked noodles to the slow cooker and gently stir to coat everything in the sauce.
Garnish & Enjoy – Sprinkle with fresh parsley and serve immediately.