Divide meringue among trays, spooning it into a mound in the centre of each lined baking tray. Using a palette knife or back of a spoon, spread meringue to make rough 20cm circles. Place trays in oven, bake for 30 minutes, then swap trays: move bottom tray to middle shelf, middle tray to top shelf and top tray to bottom shelf. Bake for a further 30 minutes. Cool overnight.