Sieve flour and icing sugar into a bowl. Add the egg whites, working the mixture together to form a smooth paste. Gradually incorporate the soft butter, mixing well. Allow the dough to rest in the fridge for at least 2 hours. Using a Stanley knife cut a triangular shape out of an ice cream container lid. Position the template on a Teflon sheet or baking tray. Using a palette knife spread the mixture within the template to 2mm thick. Repeat to desired number of tuiles. Bake the tuiles for 6 minutes or until lightly coloured. Remove from the oven and while they are hot use the palette knife to lift them from the tray and drape them over a rolling pin to achieve the desired shape and leave to cool. Once firm stir in an air tight container until required.