Preheat oven to 375°F and grease a 9x13-inch baking dish.
Boil noodles in salted water to just shy of al dente; drain well.
Heat oil in a large skillet; brown meatballs until golden and heated through.
Melt butter in the same skillet and cook onion until soft and translucent.
Stir in garlic and cook until fragrant, about 30 seconds.
Sprinkle in flour and whisk for one minute to form a roux.
Slowly whisk in broth, Worcestershire, and mustard; simmer until thick and glossy.
Remove from heat; whisk in sour cream, allspice, nutmeg, salt, and pepper.
Toss noodles, meatballs, and most parsley with the sauce until coated.
Spread mixture in the dish and sprinkle evenly with cheese.
Bake until bubbly and lightly browned, 18 to 22 minutes.
Rest five minutes, then garnish with remaining parsley and serve.
Notes
Variation: Stir in sautéed mushrooms or swap Swiss for mozzarella or provolone. Use half beef, half pork meatballs for richer flavor. Storage: Refrigerate up to 4 days; reheat covered at 350°F until hot. Freeze up to 2 months.This recipe is an original creation inspired by classic Delish Swedish Meatball Noodle Bake flavors. All ingredient ratios and instructions are independently developed.