Add the cream of mushroom soup, beef broth, Worcestershire sauce, Dijon mustard, garlic powder, onion powder, black pepper, and nutmeg to a 4- to 6-quart slow cooker. Whisk until smooth.
Add the frozen meatballs and stir gently to coat.
Cover and cook on LOW for 4–6 hours or HIGH for 2–3 hours, until the meatballs are heated through and the sauce is bubbling.
About 15 minutes before serving, cook the egg noodles according to package directions. Drain well.
Turn the slow cooker to WARM or turn off the heat. Stir in the sour cream until smooth and combined.
Serve the Swedish meatballs and sauce over the cooked egg noodles.
Notes
Sour cream: Stir the sour cream in after switching the slow cooker to WARM or turning off the heat. Adding it over high heat can cause the sauce to curdle.Storage: Store leftover Swedish meatballs, gravy, and egg noodles in an airtight container in the refrigerator for 3 to 4 days. Reheat individual portions in the microwave or warm them gently on the stovetop, adding a small splash of beef broth if the gravy has thickened.Freezer: You can freeze the meatballs and gravy for up to 3 to 4 months, but sour cream sauces can change slightly in texture after freezing. For the best results, freeze the meatballs and sauce separately from the egg noodles, thaw overnight in the refrigerator, and reheat gently while stirring.