1. In a large mixing bowl, combine the ground beef, breadcrumbs, Parmesan, egg, minced onion, minced garlic, Worcestershire sauce, salt, and black pepper. Mix gently with your hands or a fork until just combined—do not overwork the meat.

2. Roll the mixture into 18–20 meatballs, about 1 to 1 1/2 inches in size, and place them on a plate or tray.

3. Heat the olive oil in a large deep skillet over medium-high heat. Add the meatballs in a single layer, working in batches if needed, and brown on all sides until nicely caramelized and almost cooked through. Transfer the browned meatballs to a clean plate.

4. Reduce the heat to medium and add the butter to the same skillet. Once melted, add the sliced mushrooms and onions. Cook, stirring occasionally, until the mushrooms release their moisture and turn golden and the onions are very soft.

5. Stir in the minced garlic for the sauce and cook for about 30 seconds, just until fragrant.

6. Sprinkle the flour over the vegetables and stir to coat. Cook for 1 minute to remove the raw flour taste.

7. Slowly pour in the beef broth while stirring, scraping up the browned bits from the bottom of the skillet. Add the Dijon mustard, paprika, and dried thyme, stirring until combined.

8. Bring the sauce to a gentle simmer and cook for 3–5 minutes, or until slightly thickened to a gravy-like consistency.

9. Return the browned meatballs and any accumulated juices to the skillet, nestling them into the sauce. Cover and simmer on low for 8–10 minutes, or until the meatballs are fully cooked through.

10. Turn the heat to low and stir in the sour cream until the sauce is smooth and creamy. Do not let it boil after adding the sour cream to prevent curdling.

11. Taste and adjust the seasoning with additional salt and pepper if needed.

12. Serve the meatballs and sauce over warm cooked egg noodles and garnish with chopped fresh parsley.