Funny that I am just tucking into the same right now.
Make the potato mix quite dry so it more resembles pastry and pat it onto a sprayed baking sheet, make base as thin as can without making holes,spray with spraylight and bake as hot as posssible for 10 mins or so,turn over spray again and cook a bit longer till crisp and dry. Today I added a finely chopped red onion to base ,OMG is is fab.good luck with next one.