01 - In a large bowl, combine breadcrumbs with milk and let stand for 5 minutes to soften.
02 - Add ground beef, ground pork, onion, garlic, egg, salt, black pepper, allspice, and nutmeg to the bowl. Gently mix until just combined, avoiding over-mixing.
03 - Form mixture into small balls, each about the size of a walnut (approximately 1 1/4 inch diameter).
04 - Heat butter and oil in a large skillet over medium heat. Fry the meatballs in batches, turning occasionally, until browned on all sides—about 8 minutes per batch. Transfer to a plate and set aside.
05 - Melt butter in the same skillet over medium heat. Sprinkle in the flour and cook, whisking constantly, for 1 minute.
06 - Gradually pour in stock while whisking to prevent lumps. Stir in heavy cream, soy sauce, and Dijon mustard. Simmer until the sauce thickens, about 5 to 7 minutes.
07 - Return browned meatballs to the skillet, coating them with the sauce. Simmer gently for 5 to 10 minutes until meatballs are cooked through and heated completely.
08 - Serve meatballs hot, ideally accompanied by mashed potatoes, lingonberry jam, and steamed vegetables.