01 - In a large bowl, combine breadcrumbs and milk. Allow mixture to stand for 5 minutes until fully absorbed.
02 - Add ground beef, ground pork, finely chopped onion, minced garlic, egg, salt, pepper, allspice, and nutmeg to the breadcrumb mixture. Gently mix until just combined, ensuring the blend is even but not overworked.
03 - Roll the meat mixture into small, walnut-sized balls, approximately 1 1/4 inches in diameter.
04 - Heat unsalted butter and vegetable oil in a large skillet over medium heat. In batches, cook the meatballs, turning occasionally, until browned on all sides and almost cooked through, about 8 minutes. Remove meatballs and set aside on a plate.
05 - Melt unsalted butter in the same skillet over medium-low heat. Sprinkle in flour and whisk constantly, cooking for 1 minute until a light roux forms.
06 - Gradually pour in beef or vegetable stock while whisking to prevent lumps. Stir in heavy cream, soy sauce, and Dijon mustard. Adjust seasoning with salt and black pepper if needed. Simmer the sauce until thickened, about 5 to 7 minutes.
07 - Return the browned meatballs to the skillet, turning to coat evenly in the sauce. Simmer gently for 5 to 10 minutes, allowing flavors to develop and ensuring meatballs are fully cooked.
08 - Serve meatballs and sauce hot, ideally accompanied by mashed potatoes, lingonberry jam, and steamed vegetables.