Prepare the Meatballs – Mix breadcrumbs and milk in a bowl. Let sit for a few minutes. Add ground beef, pork, onion, egg, salt, pepper, allspice, and nutmeg. Mix gently until combined.
Shape the Meatballs – Roll the mixture into small balls, about 1 inch in diameter.
Cook the Meatballs – Heat butter in a large skillet over medium heat. Fry meatballs until browned on all sides. Remove and set aside.
Make the Gravy – In the same skillet, melt butter. Stir in the flour and let it cook for a minute. Slowly add beef broth while stirring. Pour in the heavy cream, then mix in the Dijon mustard and Worcestershire sauce. Simmer until thick.
Combine and Serve – Return meatballs to the skillet. Simmer for 5 minutes. Pair with mashed potatoes and a side of lingonberry jam.