From the Super Mario Wiki
The Potato Salad is an item that is found in Paper Mario. It looks like a portion of mashed potatoes with potato peel in it, on top of a few leaves of salad and is served in a gray bowl.
The Item can be obtained by getting an Iced Potato from the Toad House in Shiver City and bringing it to the Toad chef Tayce T., who will cook it then. Potato Salad is a recovery item usable inside and outside of battles and will recover ten HP when used. It also can be cooked together with a Shroom Steak to get a Deluxe Feast.