This pie is for those who love sweet and tart lemon desserts. The filling is somewhere between a lemon curd and a lemon marmalade. This recipe is based on one I found in the American food magazine "Saveur".
For the filling: thoroughly wash and dry lemons. Finely grate lemon zest into a bowl. Using a mandoline or a sharp knife, slice lemons very thinly; remove and discard seeds. Add slices to the zest and toss with the sugar and salt. Cover and set aside at room temperature for 24 hours.
For the pastry: Sift together flour and salt into a mixing bowl. Use a pastry cutter to work the butter into the flour. Sprinkle in up to 5 tbsp of cold water, stirring dough with a fork until it just begins to hold together. Press dough firmly into a rough ball, then transfer to a lightly floured surface. Give the dough several kneads with the heel of your hand to form it into a smooth ball. Divide into two, wrap in plastic and refrigerate for 1 hour.
Preheat oven to 210°C. Whisk eggs in a bowl until frothy. Add butter and flour, whisking until smooth. Stir into the lemon mixture.
Roll out dough on a lightly floured surface into two rounds large enough for a 23cm pie dish. Fit in one round and pour in the filling. Cover the pie with the remaining pastry. Fold edges under and crimp. Cut steam vents into the top crust.
Bake until the edges begin to brown, approximately 30 minutes. Reduce the heat to 180°C and bake until crust is golden brown, about 25-30 minutes more. Remove from the oven and cool on a rack for at least 30 minutes before slicing.