Asparagus with Asparagus Sauce

This recipe was inspired by an asparagus sauce served with grilled duck foie gras that I ate in Michel Guérard’s restaurant at Eugénie-les-Bains. Guérard’s sauce was made with lukewarm asparagus, mounted with vinegar and oil, and pureed in an electric blender. My sauce, a puree of asparagus skins mounted with butter, is served warm over freshly cooked large asparagus spears. It can also be used to coat a mixture of other springtime vegetables, such as baby carrots, turnips, mushroom caps, a