01 - In a large bowl, combine breadcrumbs and milk. Allow to stand for 5 minutes so the crumbs absorb the liquid.
02 - Add ground beef, ground pork, finely chopped onion, garlic, egg, salt, black pepper, allspice, and nutmeg to the bowl. Mix until just integrated without overworking the meat.
03 - Roll the mixture into small meatballs, each roughly 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, until browned on all sides—about 8 minutes. Remove meatballs and drain on paper towels.
05 - Melt butter in the same skillet. Whisk in flour and cook, stirring, for 1 minute to develop a roux.
06 - Gradually pour in stock while whisking constantly to avoid lumps. Stir in heavy cream, soy sauce, and Dijon mustard. Simmer, stirring, until the sauce thickens, about 5 to 7 minutes.
07 - Return meatballs to the skillet, spooning sauce over to coat evenly. Simmer gently for 5 to 10 minutes until the meatballs are heated through and infused with flavor.
08 - Serve hot, accompanied by mashed potatoes, lingonberry jam, and steamed vegetables if desired.