Garlicky Tortellini Soup With Sausage, Tomatoes, and Spinach
1 (10 ounce) package fresh spinach, coarsely … 1 (14 ounce) can chicken broth 1 (14 ounce) can diced tomatoes 1 (32 ounce) carton chicken broth 1 medium onion, finely chopped 1 pinch salt and ground black pepper to taste 1 pound frozen cheese tortellini 1 pound mild sausage, removed from casings 10 leaves fresh basil, chopped 6 cloves garlic, finely chopped ½ cup grated Parmesan cheese, or as needed ½ teaspoon red pepper flakes, or to taste