01 - Combine breadcrumbs and milk in a large mixing bowl and let stand for 5 minutes to absorb.
02 - Add ground beef, ground pork, finely chopped onion, minced garlic, egg, salt, black pepper, allspice, and nutmeg to the soaked breadcrumbs. Mix gently until just incorporated.
03 - Form the mixture into walnut-sized balls, approximately 1 1/4 inches in diameter, ensuring uniform size for even cooking.
04 - Heat butter and oil in a large skillet over medium heat. Sear meatballs in batches, turning occasionally, for about 8 minutes until evenly browned. Transfer cooked meatballs to a plate and set aside.
05 - Melt butter in the same skillet over medium heat. Whisk in flour and cook, stirring constantly, for 1 minute until lightly golden.
06 - Gradually whisk in beef or vegetable stock, ensuring the mixture remains smooth. Stir in heavy cream, soy sauce, and Dijon mustard. Simmer, stirring frequently, until thickened, about 5 to 7 minutes.
07 - Return browned meatballs to the skillet with the sauce and gently toss to coat. Simmer on low heat for 5 to 10 minutes until meatballs are thoroughly heated and fully cooked.
08 - Serve meatballs hot with the creamy sauce. Accompany with mashed potatoes, lingonberry jam, and steamed vegetables for a classic Swedish presentation.