Potato starch

Potato starch is the starch of the potato, sold as a fine, bright white powder. A professional pastry reference notes that it is most frequently used as a thickening agent and that it contains no gluten.

In the kitchen it can stand in for cornstarch in puddings, fruit fillings and sauces, and the same reference says it gelatinizes at about 176 F (81 C) and leaves no unpleasant taste. Because it has no gluten, a little added to bread flour lowers the dough's gluten strength, which is why bakers also stir it into cakes and shortbread-style cookies for a tender, fine crumb.

It is best added near the end of cooking, since it thickens at a fairly low temperature and gives a clear, glossy finish.