The parsnips add a creamy sweetness that complements the flavor of the split peas. If parsnips are unavailable, use carrots instead. Because the peas have a tendency to settle on the bottom of the pot, a quick stir midway through the cooking process is helpful. The Liquid Smoke adds a "bacony" flavor to the soup and is available in most supermarkets. While this is intended to be vegetarian, from Fresh From the Vegetarian Slow Cooker, I also made this with a ham bone instead of the liquid smoke and was delicious.