Preheat the oven to 375°F (190°C). Line a baking sheet with aluminum foil for easier cleanup if desired.
In a large mixing bowl, combine ground beef, ground pork, bread crumbs, Parmesan cheese, parsley, chopped onion, minced garlic, egg, salt, and black pepper. Mix until all ingredients are well incorporated.
Shape the mixture into meatballs, about 1 to 1.5 inches in diameter, and place them on the prepared baking sheet.
Bake the meatballs in the preheated oven for about 25-30 minutes or until fully cooked and browned on the outside, reaching an internal temperature of 160°F (70°C).
While the meatballs are baking, prepare the sauce. In a saucepan over medium heat, combine grape jelly and BBQ sauce. Stir until the jelly melts and the ingredients are well mixed. Bring to a simmer.
Once the meatballs are done baking, transfer them to a skillet over medium heat. Pour the grape jelly sauce over the meatballs and toss to coat.
Cook for an additional 5-10 minutes on low heat, allowing the meatballs to absorb some of the sauce flavors before serving.