Weigh the ingredients for the base and mix the butter with the soft brown sugar, lemon zest and egg until soft.
Sift the flour with the baking powder and add to the butter mixture.
Place in the refrigerator for 2 hours, then roll out to 3 mm thick.
Line the baking trays and then prick with a pastry pricker or a fork.
Bake at 190°C for 220 minutes.
Cool and store in the freezer so that they become very cold.