Combine the ground beef, ground pork, panko breadcrumbs, egg, salt, garlic powder, onion powder, allspice, nutmeg, and pepper in a large mixing bowl. Mix thoroughly with your hands, then shape into 1 ¼–1 ½-inch meatballs (approximately 25–30 pieces). Arrange the meatballs on a parchment-lined baking sheet for easy cleanup.

Heat olive oil in a large skillet or Dutch oven over medium-high heat. Fry the meatballs in two batches, turning with tongs until all sides are browned, about 5–7 minutes per batch. Add a little extra oil if needed for the second batch. Transfer the cooked meatballs to a plate.

Carefully pour off most of the fat from the skillet, leaving the browned bits for flavor. Reduce the heat to medium and melt the butter in the skillet. Stir in the flour and cook, stirring continuously, until the roux develops a golden hue.

Gradually whisk in the beef broth, ensuring the flour fully dissolves. Stir in the Dijon mustard and Worcestershire sauce. Return the meatballs to the skillet, cooking for about 10 minutes until the meatballs are fully cooked and the gravy reaches a desired consistency. Note that the gravy should remain relatively light, not overly thick.

Turn off the heat and blend in the sour cream, stirring directly into the skillet or mixing separately in a small bowl before combining. Adjust seasoning with additional salt and pepper as needed. Garnish with chopped parsley and serve immediately.