Preheat the oven to 350°F. Spray a 9×9-inch baking dish with nonstick cooking spray.
In a large bowl, combine the ground beef, ground pork, egg, Parmesan cheese, parsley, salt, and pepper. Mix until just combined.
In a separate bowl, combine the milk, breadcrumbs, garlic, and onion. Add this mixture to the meat mixture and gently mix, being careful not to overwork it.
Lightly grease your hands and form the mixture into meatballs using about 2 tablespoons per meatball. Place them into the prepared baking dish.
Bake for 20 minutes, or until the meatballs are lightly browned.
Remove from the oven and carefully drain and discard most of the grease.
In a medium bowl, whisk together the barbecue sauce, honey, and grape jelly. Pour the sauce evenly over the meatballs. Cover with foil and return to the oven. Bake for an additional 20-25 minutes, or until the meatballs reach an internal temperature of 165°F.
Serve warm.