01 - Combine breadcrumbs and milk in a large bowl. Allow the mixture to stand for 5 minutes until the breadcrumbs are moistened.
02 - Add ground beef, ground pork, onion, garlic, egg, salt, pepper, allspice, and nutmeg to the bowl. Gently mix with your hands or a spoon until just combined, taking care not to overwork the mixture.
03 - Form the combined mixture into small, round meatballs, each approximately the size of a walnut (about 1 1/4 inches in diameter).
04 - Heat butter and oil in a large skillet over medium heat. Fry meatballs in batches, turning occasionally, for about 8 minutes or until deeply browned on all sides. Transfer cooked meatballs to a plate and set aside.
05 - In the same skillet, melt butter over medium heat. Whisk in flour, stirring continuously for about 1 minute until the mixture begins to turn pale golden.
06 - Slowly pour in beef or vegetable stock while whisking to prevent lumps. Add heavy cream, soy sauce, and Dijon mustard, then stir well. Let the sauce simmer for 5 to 7 minutes until thickened.
07 - Return the browned meatballs to the skillet, coating them in the sauce. Simmer gently for 5 to 10 minutes until the meatballs are heated through and fully infused with the sauce.
08 - Serve meatballs hot over mashed potatoes, with lingonberry jam and steamed vegetables on the side if desired.