Cut the parsnips into slices. Combine them with the broth in a pot, and bring to a simmer over medium high heat. Cover the pot, lower the heat to medium-low, and simmer for about 30 minutes until the parsnips are very tender. Allow the vegetables and broth to cool slightly.
Puree the parsnips and the remaining broth (there should be about 2 cups left) in a food processor or blender. Add the sour cream and harissa and process again until smooth. Taste and adjust seasonings as needed. Serve warm.