Salsify is a long, thin, darkly earth-colored root often available in February. It is also known as "vegetable oyster" due to its subtle salt, fishy flavor, or as "poor people's asparagus." When scrubbed, the white flesh is revealed without an obvious outer skin. It can also be found preserved.
For a vegan version, substitute butter with margarine or additional oil, and use plant-based milk.
Store leftovers in an airtight container in the refrigerator for up to 3 days. Reheat gently on the stove, adding a splash of water or milk if the soup has thickened too much.