In a large mixing bowl, combine ground beef and pork, breadcrumbs, parmesan, egg, parsley, basil, sautéed minced onion, garlic cloves, salt and pepper. Mix well to combine and then shape into softball size meatballs. In a hot skillet with olive oil, brown the meatballs on all side and cook until done. (Do not overcook.)Set aside. On a floured cutting board, spread out puff pastry sheets and cut into 4-inch squares. In a bowl, mix 2 egg yolks and 2 tablespoons of water. Brush mixture over squares. Add 2-3 tablespoon of shredded mozzarella onto center of pastry square. Place meatball on top of the cheese. Wrap puff pastry around meatball, sealing with your hands. Brush more egg wash over entire dough ball and sprinkle lightly with kosher or sea salt. Place on parchment-lined baking sheet, seam side down. Brush with egg wash. Bake for 25 minutes or until golden brown. Spread marinara sauce on a plate. Add a meatball and enjoy!