Whisk together the flour and icing sugar. Whisk in the melted butter, then the egg whites. Let the mixture rest for 30 minutes in the fridge.
Preheat the oven to 180 C / Gas 4. Line a baking tray with baking parchment.
Pour a tablespoonful of the mixture onto the baking tray, and spread it into a circle with the back of a spoon. Repeat with the remaining mixture.
Bake in the preheated oven until golden at the edges, about 8 minutes. Remove from the oven to cool for 1 minute. Create the concave shape by rolling each biscuit around a rolling pin before it is completely cool, then allow to cool completely.
You can dip one end in melted dark chocolate once the tuiles are cooled. Also, you can shape the biscuits into ovals rather than circles to make a biscuit called 'langue de chat' or cat tongue.