Whisk the egg whites until they form soft peaks, before they become too firm, add the sugar and beat to obtain a firm texture.
Whisk the egg yolks and gently add them to the egg whites and the natural colouring powder.
Gently mix the whites, yolks and sifted flour with a rubber spatula.
On a baking sheet, form the cookies using a pastry bag.
Sprinkle with icing sugar before putting in the oven for 20 minutes at 160°C.
Allow to cool before storing in a small metal box.