1. In a large mixing bowl, combine the ground beef, ground pork, breadcrumbs, egg, onion, garlic, parsley, allspice, nutmeg, salt, and pepper. Mix gently to ensure even distribution of ingredients without overworking the meat.
2. Form small, uniform-sized meatballs, around 1 to 2 inches in diameter, rolling them gently between your palms.
3. Arrange the meatballs on a baking sheet and chill them in the refrigerator for at least 15 minutes to help maintain their shape during cooking.
4. Heat a large skillet over medium heat, adding a mixture of butter and olive oil. When the skillet is hot, begin frying the meatballs in batches, ensuring they are browned on all sides. This should take about 6-7 minutes per batch.
5. Remove the cooked meatballs from the skillet and set aside. To prepare the sauce, use the remaining oil in the skillet.
6. Melt butter in the same skillet and whisk in flour to create a roux. Slowly add beef broth while continuing to whisk, allowing the mixture to thicken.
7. Add the heavy cream, Worcestershire sauce, and Dijon mustard to the roux. Simmer on low heat, stirring occasionally until the gravy reaches the desired consistency. Season with salt and pepper to taste.
8. Return the meatballs to the skillet, gently stirring to coat them in the sauce. Let them simmer for an additional 10 minutes to absorb the flavors.
9. Serve the meatballs hot, optionally over egg noodles or mashed potatoes, garnished with parsley. Enjoy your delicious Swedish Meatballs!