Gather all ingredients. Preheat the oven to 425 degrees F (220 degrees C).

Whisk together sour cream and cream cheese in a 9x13-inch baking dish until smooth. Gradually whisk in broth. Stir in Worcestershire sauce, mustard, salt, and pepper.

Stir in mushrooms, onion, and garlic.

Fold in noodles and meatballs; lightly press with the back of a spoon to submerge noodles in the liquid as much as possible.

Cover dish tightly with foil and bake in the preheated oven for 30 minutes.

Remove from the oven and stir mixture, pressing noodles down again to submerge in the mixture. (If some noodles look underdone at this point, it’s fine, they will get done while it finishes baking and standing.)

Top with French-fried onions. Bake uncovered until topping is golden and mixture is heated through, 10 minutes more.

Let sit for 10 minutes before serving. Garnish with chopped parsley.