Kosher salt and freshly ground black pepper, to taste
1. Heat 1 tablespoon olive oil in a large skillet over medium heat. Add onion, and cook, stirring frequently, until onions have become translucent, about 2-3 minutes.
2. In a large bowl, combine ground beef, ground pork, Panko, egg yolks, allspice, nutmeg and cooked onion; season with salt and pepper, to taste. Using a wooden spoon or clean hands, stir until well combined. Roll the mixture into 1 1/4-to-1 1/2-inch meatballs, forming about 24 meatballs.
3. Add remaining 1 tablespoon olive oil to the skillet. Add meatballs, in batches, and cook until all sides are browned, about 4-5 minutes. Transfer to a paper towel-lined plate.
4. Serve immediately, garnished with parsley, if desired.