How to cook
Whisk the eggs with the sugar and add them to the ammonium bicarbonate and baking soda that you've dissolved in the yoghurt in advance. Mix and add the butter, lemon zest and finally the sifted flour. Knead a smooth dough.
Tear pieces from it and shape rolled balls or roll it out and cut out your desired cookie shapes. Arrange them on a tray with baking paper. Top them with a mixture of beaten egg yolk with a little oil, ground walnuts and sprinkle each cookie with a little crystallized sugar.
Put them to bake in a moderate oven up to a nice tan.