1. Place a foil-lined jelly-roll pan in oven on the middle rack. Preheat oven to 450° (keep pan in oven).
2. Cook noodles according to the package directions, omitting salt and fat. Drain; keep warm.
3. Heat a large skillet over medium-high heat. Add 2 teaspoons oil to pan; swirl to coat. Add onion to pan; sauté 6 minutes or until tender. Place onion in a small bowl. Combine beef, 3 tablespoons parsley, panko, milk, 1/4 teaspoon salt, and 1/4 teaspoon pepper in a large bowl; stir in 1/3 cup cooked onion. Shape beef mixture into 16 (1 1/2-inch) meatballs. Place meatballs on preheated pan coated with cooking spray. Bake at 450° for 12 minutes or until done, turning after 6 minutes.
4. Return skillet to medium-high heat. Add remaining 2 teaspoons oil to pan; swirl to coat. Add mushrooms, garlic, and paprika to pan; sauté 8 minutes or until mushrooms are lightly browned. Add wine to pan; cook 1 minute or until liquid almost evaporates. Sprinkle flour over mushroom mixture; cook 30 seconds, stirring constantly. Add stock; bring to a boil, scraping pan to loosen browned bits. Reduce heat, and simmer 3 minutes or until sauce slightly thickens. Stir in remaining cooked onion; remove pan from heat. Stir in remaining 1/4 teaspoon salt, remaining 1/4 teaspoon pepper, sour cream, mustard, and nutmeg. Add meatballs to sauce; toss to coat. Spoon sauce and meatballs over cooked noodles. Sprinkle evenly with remaining parsley.
Wine note: Go for a citrusy and mildly floral white, like A to Z's Oregon Pinot Gris, 2012 ($12). This crisp, full-bodied wine has enough structure to stand up to the meatballs and plenty of racy sharpness to complement the tangy combination of sour cream, garlic, and mustard. --Jordan Mackay