inches a small bowl, combine bread crumbs and milk; let stand 10 minutes.
In large bowl, combine prosciutto, beef, pork, eggs, cheese, parsley, oregano, 3 tablespoons basil, 3 minced garlic cloves, 1 teaspoons salt, and 1/2 teaspoons pepper. Add soaked bread crumbs and mix gently until combined. Divide into 1/4 cup portions; roll into balls. Set on parchment paper-lined baking sheet.
Heat 2 tablespoons oil in 11" skillet over medium-high heat. Working in 2 batches, brown meatballs on all sides, about 8 minutes per batch. Transfer to plate.
In same pan, warm 3 tablespoons oil over medium heat. Cook onion, stirring occasionally, until softened, about 8 minutes. Add 2 minced garlic cloves, cook one minute, Add tomatoes and juices; season with salt and pepper. Bring to a simmer; cook until sauce thickens, about 20 minutes. Stir in 3 tablespoons basil. Add meatballs; cook, turning occasionally and basting with sauce, until cooked through, about 30 minutes. Transfer to platter.