Tortellini Soup with Italian Sausage and Kale

Ingredients

• pound mild italian sausage, ground or casing removed
• medium yellow onion, chopped
• garlic cloves, minced
• quart chicken stock
• can crushed tomatoes
• tablespoons tomato paste
• teaspoon sea salt
• bunch curly kale, stemmed and roughly torn
• ounces fresh tortellini
• heavy cream
• Parmesan cheese, grated for serving
• teaspoon red pepper flakes, for serving