In a large mixing bowl, combine ground beef, ground pork, breadcrumbs, egg, milk, minced onion, minced garlic, salt, pepper, allspice, and nutmeg until well incorporated.
Roll the mixture into approximately 24-28 meatballs of 1-inch diameter.
Heat 2 tablespoons of butter in a large skillet over medium-high heat.
Brown the meatballs on all sides in the skillet until fully cooked through, approximately 8-10 minutes. Remove meatballs and set aside.
Reduce heat to medium and add the remaining 3 tablespoons of butter to the skillet drippings.
Whisk in the all-purpose flour and cook for 1-2 minutes until the roux reaches a light golden color.
Gradually pour in beef broth while whishing constantly to prevent lumps.
Add Worcestershire sauce and Dijon mustard, then simmer until the sauce thickens.
Stir in heavy cream and return the meatballs to the skillet.
Simmer for 3-5 minutes to heat the meatballs through and coat them thoroughly in the sauce.