Preheat oven to 400 degrees F. Line a baking sheet with parchment paper.
In a large bowl, combine ground beef, Italian sausage, onion, Panko, milk, egg, Parmesan, parsley, garlic and basil; season with 1 teaspoon salt and 1/2 teaspoon pepper. Using a wooden spoon or clean hands, stir until well combined. Roll the mixture into 3/4-inch meatballs, about 1 tablespoon per meatball, forming about 45 meatballs.
Place meatballs in a single layer onto the prepared baking sheet. Place into oven and bake until cooked through, about 15 minutes; set aside.
for the soup
Heat olive oil in a large stockpot or Dutch oven over medium heat. Stir in garlic, onion and Italian seasoning. Cook, stirring frequently, until onions have become translucent, about 2-3 minutes; season with salt and pepper, to taste.
Whisk in flour until lightly browned, about 1 minute.
Stir in chicken stock, tomato sauce and Parmesan rind, if using. Stir in meatballs. Bring to a boil; reduce heat and simmer, covered, until flavors have blended, about 10 minutes.
Stir in pasta and cook until tender, about 8 minutes.
Stir in kale until wilted, about 1-2 minutes. Stir in basil; season with salt and pepper, to taste.