Curdled? If the sauce "curdles", it's easily fixable. Remove the cup from the water bath. In another bowl, pour in a couple Tbsp of boiling water to heat the bowl. When the bowl is warm, dump the water out and add a new Tbsp of boiling water. Then, whisking vigorously, slowly pour the sauce into the Tbsp of hot water. As you whisk, it will recongeal and the curdles will disappear.