Potato starch often appears in gluten-free recipes as a thickener instead of flour. Finding potato starch at a grocery store can be difficult, but you can make your own at home. For the best results, use a large, high starch russet (baking) potato to make your homemade starch. The final amount of starch made from this process varies with the age and type of potato used.
Line a colander with two layers of cheesecloth, and place the colander over the bowl.
Grate the potato with the smallest set of holes on your grater into the cheesecloth.
Fold the ends of the cheesecloth up and over the potatoes to cover.
Press down on the cheesecloth until the starchy liquid from the potatoes drains into the bowl.
Open the cheesecloth and pour ½ cup of water over the potatoes.
Reclose the cheesecloth and squeeze the potatoes.
Repeat steps 5 and 6 with the remaining ½ cup water.
Place the two cans on top of the cheesecloth and leave them on top of the cheesecloth to squeeze more starch from the potatoes for 1 to 2 hours.
Remove the colander and discard the cheesecloth with the potatoes.
Carefully pour the liquid into the measuring cup from the the bowl without disturbing the starch that settled to the bottom.
Discard the liquid in the cup and use the remaining potato starch in the bowl. (see reference2)