01 - In a large mixing bowl, combine the breadcrumbs and milk. Let the mixture sit for 5 minutes to soften.
02 - Add ground beef, ground pork, onion, garlic, egg, salt, black pepper, allspice, and nutmeg to the soaked breadcrumbs. Gently mix by hand until evenly incorporated, being careful not to overwork the mixture.
03 - Form the mixture into small, walnut-sized balls—about 1 1/4 inches in diameter.
04 - In a large skillet, heat unsalted butter and vegetable oil over medium heat. Fry the meatballs in batches, turning frequently, until evenly browned on all sides, about 8 minutes total. Remove the browned meatballs and set aside.
05 - In the same skillet, melt unsalted butter over medium heat. Add all-purpose flour and whisk continuously for 1 minute to create a smooth roux.
06 - Gradually pour in beef or vegetable stock while whisking to avoid lumps. Stir in heavy cream, soy sauce, and Dijon mustard. Simmer the sauce, stirring often, until it thickens to a creamy consistency, about 5 to 7 minutes.
07 - Return the browned meatballs to the skillet, turning to coat them in the sauce. Simmer gently for 5 to 10 minutes until the meatballs are thoroughly heated.
08 - Serve the meatballs smothered in cream sauce, accompanied by mashed potatoes, lingonberry jam, and steamed vegetables if desired.