Earthy parsnips are sweetened with apples and blended into a delightfully silky puree.
Melt 2 tablespoons butter in a large heavy skillet over medium heat. Cook parsnips in a single layer until just golden on bottoms, about 10 minutes. Flip, and add apples, water, and 1 1/4 teaspoons salt. Raise heat to medium-high, and simmer, covered, until parsnips and apples are very soft, about 20 minutes.
Remove from heat, and let stand, covered to retain moisture, until slightly cooled, about 5 minutes. Puree mixture in a blender until smooth. With machine running, add remaining tablespoon butter.
Storage: Mash can be refrigerated for up to 2 days. Reheat before serving.