01 - Combine breadcrumbs and milk in a large bowl and let stand for 5 minutes to allow the mixture to absorb.
02 - Add ground beef, ground pork, chopped onion, minced garlic, egg, salt, black pepper, allspice, and nutmeg to the bowl. Mix gently until just combined—avoid over-working the mixture to maintain tenderness.
03 - Using moistened hands, form the mixture into small balls, each about the size of a walnut or roughly 1 1/4 inches in diameter.
04 - Heat unsalted butter and vegetable oil in a large skillet over medium heat. Fry meatballs in batches until golden brown on all sides, about 8 minutes, turning them occasionally. Remove from skillet and set aside on a plate.
05 - Melt butter in the same skillet over medium heat. Sprinkle in the flour, whisking constantly, and cook for 1 minute to form a smooth roux.
06 - Gradually pour in stock while whisking to avoid lumps. Blend in heavy cream, soy sauce, and Dijon mustard. Bring to a simmer and cook until the sauce thickens, about 5 to 7 minutes. Season with salt and pepper to taste.
07 - Return the browned meatballs to the skillet, turning gently to coat them in the sauce. Simmer over low heat for 5 to 10 minutes until the meatballs are cooked through and heated throughout.
08 - Present hot, ideally with mashed potatoes, lingonberry jam, and steamed vegetables.