Mix the flour, lemon zest and salt in a bowl. Add the butter and rub together using your hands to form an even, crumbly mixture. Add the orange peel, mix. Beat the egg white, icing sugar and vanilla paste well, add and quickly combine to form a soft dough. Shape into a roll approx. 4 cm in diameter, cover and chill for approx. 1 hr.
Shape the dough, in batches, into rolls the width of your finger, cut into pieces approx. 3 cm long. Shape into crescents and place on two baking trays lined with baking paper.
Bake each tray for approx. 12 mins. in the centre of an oven preheated to 200°C. Remove from the oven, allow to cool a little, then leave to cool completely on a rack.
Pour the icing into a bowl. Dip one end of each crescent into the icing, all the excess to drip off then place on a rack, then on baking paper. Cover and chill for approx. 30 mins.