Garlicky Tortellini Soup With Sausage Tomatoes and Spinach

Ingredients

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