Preheat the oven to 425°F (220°C).
Line baking sheets with parchment paper.
Beat the egg whites until softly peaked, then beat in the sugar until the mixture makes a stiff meringue.
In a separate bowl, beat the egg yolks until they are thick and light.
Fold 1/3 of the egg white mixture into the egg yolks.
Sift the flour over this mixture and fold it in, then fold in the remaining egg whites.
Spoon the batter in strips about 1 x 3 inches (2.5 x 7.5 cm) onto the prepared baking sheets or, using a pastry bag with a plain ½ inch (1.3 cm) tip, pipe the batter onto the baking sheets.
Bake 5 to 7 minutes, until the cookies are lightly colored.
Allow them to cool before removing them from the paper.