Heat 1 tablespoon olive oil in a large skillet over medium heat. Add diced onion and sauté until translucent, 2–3 minutes. Set aside.
In a large bowl, combine ground beef, pork, breadcrumbs, yolks, onion, allspice, nutmeg, salt, and pepper. Mix until just combined.
Form into 1.5-inch meatballs (about 20–24 total).
Heat remaining oil in skillet and brown meatballs in batches, 4–5 minutes each side. Transfer to a plate.
In same skillet, melt butter. Whisk in flour and cook until golden.
Gradually whisk in beef broth; cook until thickened, about 2 minutes.
Stir in sour cream, season with salt and pepper. Return meatballs to skillet and simmer 8–10 minutes.
Serve hot over egg noodles or rice. Garnish with parsley.
