In a large bowl, combine the ground beef, ground pork, breadcrumbs, egg, milk, allspice, nutmeg, garlic powder, onion powder, salt, and black pepper. Mix gently until just combined. Roll the mixture into roughly 30 meatballs, about 1.5 inches each.
Place the meatballs in the slow cooker in a single layer, stacking a second layer on top if needed.
In a bowl, whisk together beef broth, soy sauce, and dijon mustard. Pour the liquid over the meatballs.
Cover and cook on low for 5 to 6 hours or on high for 3 hours, until the meatballs are fully cooked through.
In a small bowl, whisk the cornstarch with 3 tablespoons of cold water until smooth. Stir the slurry gently into the slow cooker.
Pour in the heavy cream and gently stir to combine. Cover and cook on high for 15 to 20 minutes until the sauce is thick and glossy.
Serve the meatballs and sauce over cooked egg noodles, garnished with fresh parsley.