Salsify in Lemon Sauce

Virtually all early American cookbooks contained recipes for stewed salsify, a much-favored vegetable and presentation. Some recommended cooking the salsify in vinegar, water, butter, and a little sugar and salt, to which egg yolks were added at the end as thickener and enrichment. The sauce that follows is between that and the Greek avgolemono, stabilized with a little starch to permit final cooking with the salsify without curdling.