In a large mixing bowl, combine ground beef, ground pork, egg, panko breadcrumbs, salt, garlic powder, onion powder, allspice, nutmeg, and black pepper. Mix thoroughly using your hands until all ingredients are well incorporated. Form the mixture into 1¼ to 1½-inch meatballs, approximately 25-30 pieces, and set them aside on a clean plate.

Heat 2 tablespoons of olive oil in a large skillet over medium-high heat. Once hot, carefully add half of the meatballs to the skillet, frying them for about 5-7 minutes until all sides are nicely browned. Transfer the meatballs to a clean plate and repeat with the remaining batch.

Drain the excess oil from the skillet while preserving the browned bits at the bottom. With the heat still on medium, add 2 tablespoons of butter to the skillet. Let it melt completely.

Sprinkle in 2 tablespoons of flour, stirring continuously. Cook this roux for about 2-3 minutes until it turns a light golden color.

Gradually whisk in 2 cups of beef broth, ensuring there are no lumps. Continue stirring until the gravy is smooth and starts to thicken, around 3-5 minutes. Then, add 1 tablespoon of Dijon mustard and 1 tablespoon of Worcestershire sauce, mixing well.

Return the browned meatballs to the skillet, gently stirring to coat them in the gravy. Lower the heat to a simmer and let them cook for about 10 minutes, ensuring they reach an internal temperature of 165°F.

Remove the skillet from heat and stir in 1 cup of full-fat sour cream until well blended. Adjust seasoning with salt and pepper as needed.

Spoon the creamy meatballs over mashed potatoes or egg noodles. Garnish with freshly chopped parsley and serve immediately.