Tortellini Soup

Ingredients (17)

• 1 tablespoon (15ml) extra-virgin olive oil
• 1 1/2 pounds mild or spicy Italian sausage, removed from casing
• 1 medium onion (8 ounces; 227g), finely chopped
• 3 medium cloves garlic (1/2 ounce; 15g), finely chopped
• 3 medium celery ribs (about 5 3/4 ounces; 165g) with leaves, finely chopped
• 1 large carrot (about 2 3/4 ounces; 75g), finely chopped
• 1 medium fennel bulb (8 ounces; 226g), finely chopped
• 1 1/2 teaspoons fennel seeds
• 1/4 teaspoon crushed red pepper flakes (optional)
• 1/4 cup tomato paste (3 1/2 ounces; 100g)
• 1/4 cup all-purpose flour (about 1 ounce; 32g)
• 6 cups (1.4L) homemade chicken or vegetable stock or store-bought low-sodium broth
• 4 ounces lacinato or curly kale or other hardy greens, such as collards or Swiss chard (about 113g; 2 cups)
• 1 cup (240ml) heavy cream
• 6 ounces (170g) fresh or frozen cheese tortellini
• Pesto, homemade or store-bought, for serving (optional)
• Grated Parmigiano-Reggiano, for serving (optional)