In a large bowl, combine ground beef, ground pork, breadcrumbs, egg, salt, pepper, nutmeg, and allspice. Mix well.
Form the mixture into small meatballs.
Heat olive oil in a large skillet over medium heat. Brown the meatballs on all sides.
Transfer the browned meatballs to the slow cooker.
In a mixing bowl, whisk together beef broth, heavy cream, flour, soy sauce, and Dijon mustard.
Pour the gravy mixture over the meatballs in the slow cooker.
Cover and cook on low for 4 hours.
Serve the meatballs with gravy over mashed potatoes or egg noodles.