01 - Combine breadcrumbs and milk in a large mixing bowl and let stand for 5 minutes.
02 - Add ground beef, ground pork, chopped onion, minced garlic, egg, salt, pepper, allspice, and nutmeg to the bowl. Mix just until evenly combined, avoiding overworking the mixture.
03 - Form mixture into small balls, each approximately the size of a walnut (about 1 1/4 inch diameter).
04 - Heat unsalted butter and vegetable oil in a large skillet over medium heat. Sear meatballs in batches until browned on all sides, about 8 minutes total, turning occasionally. Transfer to a plate as they finish.
05 - Melt unsalted butter in the same skillet. Add flour, whisking constantly, and cook for 1 minute until lightly golden.
06 - Gradually whisk in stock to prevent lumps. Stir in heavy cream, soy sauce, and Dijon mustard. Simmer over medium-low heat until the sauce is thickened, about 5 to 7 minutes.
07 - Return meatballs to the skillet, gently turning to coat with sauce. Simmer for 5 to 10 minutes until meatballs are fully heated through.
08 - Serve meatballs hot, garnished with sauce, ideally accompanied by mashed potatoes, lingonberry preserves, and steamed vegetables.