Add potatoes, water, capers, and olives. Cover, lower heat to medium and cook, stirring occasionally, until potatoes are barely soft, about 7 minutes. Remove cover and cook until all liquid evaporates. Dissolve sugar in vinegar and pour over potatoes. Serve warm or chilled.
Flavor is enhanced is the dish is refrigerated for a couple of days.
Drain and mash. Combine mashed potatoes with butter, salt, pepper, and onion. It's not necessary to cool the crust before filling and rebaking. Toss the potato strips in the oil. Shake off any excess oil, then place the strips on an ungreased baking pan.