Potato, carrot and hard-boiled egg in mayonnaise. Three ingredients plus the dressing, and the only work is boiling things and waiting for them to cool. Serves three.
Everything has to be cold before the mayonnaise goes in. Mayonnaise is an emulsion of oil and egg, and warm potato splits it into a greasy, separated mess. Boil, drain, and let it all cool completely, ideally in the fridge. Twenty minutes is longer than a hard-boiled egg needs, and it is what causes the grey-green ring around the yolk: ten minutes then straight into cold water avoids it, though the ring is harmless. A waxy potato holds its cubes and a floury one crumbles into the mayonnaise, which some people prefer.