Set to 150c or lower and watch them like a hawk. Once they flatten out or close to, then put between to sheets of glass and let cool. The secret is don't cook them to the point they bubble. If your not happy with the first result, try it again. Better a couple of small goes than one long failure. I have cooked too long and its not pretty and the difference between perfect and disaster can be a matter of seconds. So watch all the time