To make the pastry base

1. Using a pastry cutter or in a food processor blend together the butter sugar and flour.
2. Press evenly into the bottom of a greased and parchment paper lined 9×13 inch baking pan.
3. Bake for 20 to 25 minutes at 350 degrees F ( 325 degrees F if you are using glass bake-ware)

For the lime topping

1. Simply whisk together the sugar flour, eggs, zest and lime juice until the sugar is dissolved.
2. Allow the topping to sit for about 10 minutes before whisking together well again and pouring over the baked shortbread base.
3. Bake at 350 degrees F for about another 20- 25 minutes or until the top is slightly browned and the custard appears to be set. The bottom should just be beginning to brown slightly at the top edges. Cool completely. Sprinkle with icing sugar when cool or try adding a meringue topping.