Sift the flour and salt into a mixing bowl.
Rub the butter into the flour until it reaches a fine breadcrumb consistency.
Mix in the sugar, egg yolk, and a splash of cold water to form a firm dough.
Wrap the dough in film and refrigerate for 30 minutes.
Preheat the oven to 190°C and grease a 22cm fluted tin on a baking tray.
Roll out the pastry and line the tin, leaving the excess hanging over the edges.
Line with paper and beans, trim excess, and bake blind for 15-20 minutes, then lower heat to 150°C.
Mix sugar, cornflour, and water into a paste in a bowl.
Boil 50ml water and lemon zest in a pan.
Whisk the hot liquid into the cornflour paste until smooth.
Beat in the egg yolks, lemon juice, and butter, then return to the pan.
Stir over low heat until thickened and pour into the pastry case.
Whisk egg whites to stiff peaks, gradually add sugar, and pipe over the curd.
Bake for 35-45 minutes until the meringue is crisp on the outside.
Serve warm or cold in slices.