In a small bowl, soak the breadcrumbs in milk and set aside for 5 minutes.
In a large bowl, combine ground beef, ground pork, soaked breadcrumbs, egg, salt, pepper, allspice, and nutmeg. Mix thoroughly but gently until just combined.
Shape the mixture into 1-inch meatballs and set them on a plate.
Heat butter in a large skillet over medium heat and brown the meatballs on all sides. Remove meatballs and set aside.
Add flour to the skillet and whisk for 1-2 minutes to make a roux. Gradually add beef broth, whisking continuously until the gravy thickens.
Return meatballs to the skillet, cover, and simmer for 15 minutes until cooked through.
Stir in heavy cream, cook for another 5 minutes, then serve meatballs with the creamy gravy.
Notes
Serve with lingonberry sauce and mashed potatoes for an authentic Swedish meal.