01 - In a large bowl, combine breadcrumbs with milk and allow to soak for 5 minutes.
02 - Add ground beef, ground pork, onion, garlic, egg, salt, black pepper, allspice, and nutmeg to the soaked breadcrumbs. Gently mix until just incorporated, taking care not to overwork the mixture.
03 - Portion and roll the mixture into small balls, each about the size of a walnut or roughly 1 1/4 inches in diameter.
04 - Heat butter and oil in a large skillet over medium heat. Fry meatballs in batches until evenly browned on all sides, about 8 minutes total, turning occasionally. Transfer browned meatballs to a plate and set aside.
05 - In the same skillet, melt butter over medium heat. Whisk in flour and cook while stirring for 1 minute to form a roux.
06 - Gradually pour in stock, whisking constantly to prevent lumps. Stir in heavy cream, soy sauce, and Dijon mustard. Cook, stirring frequently, until the sauce has thickened, 5 to 7 minutes. Season with salt and pepper to taste.
07 - Return browned meatballs to the sauce in the skillet. Coat each meatball thoroughly and simmer gently for 5 to 10 minutes until warmed through.
08 - Serve hot, accompanied by mashed potatoes, lingonberry jam, and steamed vegetables if desired.