In a large bowl combine the beef, pork, panko, milk, egg and yolks, shallot, garlic, thyme, allspice, nutmeg, and salt and pepper. Use a spoon or fork to mix everything together until combined. Using clean hands, portion the mixture into 1 inch sized balls, making about 45 balls total (give or take a few).
In a large Dutch oven, or high sided skillet, heat the oil over medium heat. Working in batches, add some of the meatballs to the pot, cook until all sides are browned, about 5 minutes. Transfer the meatballs to a paper towel lined plate.
In the now empty Dutch oven, add the butter, once melted whisk in the flour and cook for 1 minute. Next, slowly whisk in the beef broth. Bring the sauce to a simmer. Once simmering return the meatballs to the pot. Bring the mixture to a boil, then reduce to a simmer. Cover, and let the meatballs continue cooking for about 15 minutes, or until cooked through and no longer pink inside.
Once the meatballs have finished cooking, use a slotted spoon to remove the meatballs from the sauce (I place them in a large bowl). Boil the sauce for about 4-5 minutes or until slightly reduced.
Whisk the sour cream into the sauce.
Return the meatballs to the sauce. Garnish with the chopped parsley. Serve over cooked egg noodles.