For a richer flavor, use Italian sausage with fennel. Feel free to use sweet, mild, or hot Italian sausage depending on your preference. Rinsing the lentils before cooking helps to remove any debris and ensures a cleaner flavor. Adjust the amount of chicken stock to achieve your desired soup consistency. For a thicker soup, use less stock; for a thinner soup, use more. This soup tastes even better the next day, as the flavors have more time to meld together. Store leftovers in an airtight container in the refrigerator for up to 3 days.