Lightly grease the inside of a 5–6 quart slow cooker with nonstick cooking spray.

Add the frozen fully cooked meatballs, sliced mushrooms, and diced onion to the crockpot.

In a medium bowl, whisk together the beef broth, Worcestershire sauce, minced garlic, paprika, black pepper, and salt.

Pour the seasoned broth mixture over the meatballs and vegetables. Stir gently to combine.

Cover the slow cooker with its lid and cook on LOW for 4–6 hours or HIGH for 2–3 hours, until the meatballs are thoroughly heated and the mushrooms are tender.

About 20 minutes before serving, bring a large pot of salted water to a boil.

Add the egg noodles and cook according to package instructions until tender. Drain well and set aside.

If you prefer a thicker sauce, mix the cornstarch with cold water until smooth. Stir the mixture into the crockpot, cover, and cook on HIGH for 10–15 minutes until slightly thickened.

Turn the slow cooker to LOW or WARM. In a separate bowl, mix the sour cream with a few spoonfuls of warm sauce to temper it.

Gently stir the sour cream mixture into the crockpot until the sauce becomes smooth and creamy. Avoid boiling after adding sour cream to prevent curdling.

Add the cooked egg noodles directly to the crockpot and gently toss until evenly coated with the creamy stroganoff sauce.

Allow everything to warm together for 5 minutes, adding a splash of beef broth if the sauce becomes too thick.

Sprinkle with freshly chopped parsley and serve warm.