Place the parsnips, cream, and water into the sauce pot. You may need to add additional water to cover the parsnips. Bring the liquid to a simmer and cook the parsnips until they have no resistance when tested with a paring knife.

Transfer the parsnips and thickened liquid to a blender. Begin blending on low speed and gradually increase the speed. With the blender running, add the butter and season conservatively with salt. Process until the purée is extremely smooth. Stop the blender and check the seasoning, adjusting with salt if necessary. Check the consistency and adjust with additional water if necessary to your preference.