Trim the crusts from the bread and spread the slices out on a tray to dry for about 24 hours.
In the container of a food processor, place the almonds, garlic, and cooled potato. Process until smooth.
Mix the lemon juice, vinegar, olive oil, salt, and sugar in a small bowl and set aside. Fill a large bowl with cool water. Drop the dried bread into the water, 1 slice at a time. When it is soaked, squeeze about half the water from the bread between the palms of your hands. Add the bread to the ingredients in the processor, alternating with the lemon-juice mixture, and process until smooth. Since the skordalia has a tendency to stiffen and become pasty as it chills, the mixture should be quite loose at this point. Taste and adjust the seasoning. Scrape the mixture into a bowl. Cover and refrigerate for several hours to allow the flavors to mellow and blend. If the mixture seems too stiff, beat in a little water before serving.
Recipe courtesy of The Periyali Cookbook, by Holly Garrison