Grease your pan

Mix sugar with vanilla sugar in a bowl

Grate clementine skin, set aside

Mix flour with BP and salt

Separate yolk from egg white

Cream butter and sugars

Beat in the yolk with lemon juice plus grated clementine skin, until just combined

Beat in flour

Using a clean beater, beat egg white to stiff foam

Fold in egg white into batter, lightly so you wont deflate the foam

Spoon batter into pan, bake on preheated 350 F for 10-12 mins

Let stand for 15 minutes, then move cookies to cooling rack