FOR MEATBALLS
1 cup plain bread crumbs
1/4 cup whole milk, at room temperature
2 large eggs, at room temperature
1 small onion, finely chopped*
1/2 cup finely grated Parmesan cheese
1/4 cup chopped fresh basil leaves
1/4 cup chopped fresh Italian parsley leaves
1 tablespoon tomato paste
2 cloves garlic, minced
3/4 teaspoon kosher salt
1/2 teaspoon freshly ground black pepper
1 pound ground dark turkey meat
1 pound spicy Italian turkey sausage links, casings removed
Extra-virgin olive oil, for drizzling

FOR SAUCE
1/4 cup extra-virgin olive oil
1 large onion, finely chopped
1 teaspoon kosher salt
1/2 teaspoon freshly ground black pepper
3 large garlic cloves, smashed and peeled
2 teaspoons dried oregano
2 teaspoons finely ground fennel seeds
2 (28-ounce) cans crushed tomatoes
3/4 cup chopped fresh basil leaves
1/2 low-sodium chicken broth
Grated parmesan cheese