Potato starch often appears in gluten-free recipes as a thickener instead of flour. Finding potato starch at a supermarket 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 muslin, and place the colander over the bowl.
Grate the potato with the smallest set of holes on your grater into the cloth.
Fold the ends of the muslin up and over the potatoes to cover.
Press down on the muslin until the starchy liquid from the potatoes drains into the bowl.
Open the muslin and pour 125 ml (1/2 cup) of water over the potatoes.
Reclose the muslin and squeeze the potatoes.
Repeat the last two steps with the rest of the water.
Place the two weights -- food tins or other heavy items -- on top of the muslin and leave them on top of the cheesecloth to squeeze more starch from the potatoes for one to two hours.
Remove the colander and discard the muslin with the potatoes.
Carefully pour the liquid into the measuring cup from the the bowl without disturbing the starch that settled at the bottom.
Discard the liquid in the cup and use the remaining potato starch in the bowl.