01 - Combine breadcrumbs and milk in a large bowl and let stand for 5 minutes to fully hydrate.
02 - Add ground beef, ground pork, chopped onion, minced garlic, egg, salt, black pepper, allspice, and nutmeg to the breadcrumb mixture. Gently fold ingredients together until just combined, ensuring not to overwork the meat.
03 - Form the mixture into walnut-sized balls, about 1 1/4 inches in diameter, placing them on a tray.
04 - Heat unsalted butter and vegetable oil in a large skillet over medium heat. Fry meatballs in batches until golden and evenly browned on all sides, approximately 8 minutes. Transfer cooked meatballs to a plate and set aside.
05 - In the same skillet, melt unsalted butter over medium heat. Whisk in all-purpose flour and cook for 1 minute to create a roux.
06 - Gradually pour in the beef or vegetable stock while whisking continuously to avoid lumps. Stir in heavy cream, soy sauce, and Dijon mustard. Season with salt and black pepper. Simmer until thickened, about 5 to 7 minutes.
07 - Return browned meatballs to the skillet, gently turning to coat each with cream sauce. Simmer gently for 5 to 10 minutes until meatballs are heated through.
08 - Plate meatballs with cream sauce, ideally accompanied by mashed potatoes, lingonberry jam, and steamed vegetables. Serve hot.