Place the lemons into a bowl (not metal) and add the sugar.
Soak the lemon slices in the sugar for two hours or overnight, stirring from time to time.
The sugar will draw the juice out of the lemons creating a thick syrupy mixture.
While the lemons are macerating in the sugar make the pastry.
Rub the butter into flour with your fingertips till it resembles fine breadcrumbs (or whizz it in the food processor), add the salt, then add just enough cold water to form a dough.
Dust a little flour onto the bench and roll the dough and line the prepared tin.
Pop it into the freezer for 10 minutes to chill.
Beat the eggs with the tablespoon of flour until pale and fluffy and stir in the melted butter. Process the sugar and lemon slices until the lemon is very finely chopped and stir the sugary mix into the beaten eggs.
The eggs and sugar will form a zesty curd while cooking.
Pour into the prepared pastry shell and bake at 180°C for 40 – 50 minutes or until filling is no longer wobbly.
It will continue to firm as it cools. Serve dusted with icing sugar.