1. Heat half of the olive oil in a large skillet over medium heat. Add onions and garlic, cooking until soft. Set aside to cool.
2. In a large bowl, combine panko, Parmesan, whisked egg, milk, cooled onions and garlic, salt, oregano, allspice, nutmeg, and pepper.
3. Gently mix in ground beef and pork until just combined. Form mixture into 1 1/2-inch meatballs. Chill in the refrigerator for at least 15 minutes.
4. Heat the remaining olive oil in the skillet over medium-high heat. Brown meatballs in batches, removing them once browned and setting aside.
5. In the same skillet, melt butter and stir in flour; cook until lightly browned.
6. Gradually add beef broth, chicken bouillon, Worcestershire sauce, and Dijon mustard, stirring continuously until smooth.
7. Bring to a simmer and stir in heavy cream until well combined. For a smoother sauce, mix a portion with sour cream if desired.
8. Return meatballs to the skillet, spooning sauce over them. Simmer for 10-15 minutes.
9. Serve meatballs over noodles or mashed potatoes, garnishing with parsley as desired. Add lingonberry jam on the side for an authentic touch.