Add the ground beef, pork, breadcrumbs, milk, dried onions, garlic powder, salt, black pepper, nutmeg, and allspice to a large bowl. Mix until just combined (overworking/mixing may result in less juicy meatballs).
Form 2-inch meatballs from the meat mixture and set them aside on a large tray.
Heat a large skillet with oil (approximately 2-3 tablespoons) over medium-high heat. Add as many meatballs to the skillet that will fit comfortably without crowding. Fry the meatballs until they begin the brown on each side. (They won’t be cooked all the way through at this point, we just want to get a nice color on them for now.)
Transfer the browned meatballs to a clean plate and repeat with the remaining meatballs until all the meatballs have been browned on each side. Add additional oil to the pan as needed.
To make the sauce, melt the butter (with the pan drippings) over medium heat in the same skillet that was used to brown the meatballs. Once melted, add the flour to the butter whisking well to combine. Whisk continuously for 3-5 minutes or until it has a nice golden color.
Pour in the beef broth, Worcestershire sauce, black pepper, and salt, and cook for an additional 5 minutes, stirring continuously until thickened. Then add the half-and-half and sour cream and stir until the sauce is thick and creamy, about 5 minutes.
Nestle the meatballs into the sauce, cover, and cook over medium-low heat for 8-10 minutes or until the meatballs are cooked through.
Served with mashed potatoes and garnished with fresh parsley if desired.