You can use potato starch or arrowroot starch in the same manner as corn
starch. The technique is the same. Depending on how much liquid you're
trying to thicken, try adding one teaspoon of xxxx-starch to 1/2 cup of
COLD water and immediately stir it like crazy long enough to thoroughly
dissolve it. A small wire whisk is definitely the best stirring implement;
next best is a large fork. Add it to your warm or hot pot still over heat,
stir some more, let simmer a minute or two until it thickens up. You can
repeat the mix-starch-with-cold-water process if your quantity of hot
liquid was so large that it's not getting to the thickness you want.