Carol:

I am utterly surprised that you don't have tapioca flour on hand as you are in Jakarta now... But if you must use cornstarch as a thickening, I'd say the same amount of corstarch for the tapioca flour is OK. It worked for me before... ^_^ If you dissolve cornstarch in a little cool/cold liquid first before adding into the whole glaze (or whatever you are making), it will be fine. **I normally use it as a thickening agent for sauce in the wok over very high heat(when I don't have tapioca flour). Hope this helps...