01 - 
                Preheat the oven to 180C/350F/Gas 4. In a food processor, blend plain flour and unsalted butter until the mixture resembles fine breadcrumbs. Add confectioners' sugar, beaten egg, and one tablespoon of water. Process until the dough forms a ball. Roll the dough to 3mm thickness and line a 23cm/9in flan tin. Cover and chill for 30 minutes.
              
              
              
                02 - 
                Trim excess pastry and press the top edge slightly higher than the tin. Line with parchment and fill with baking beans. Bake for 15 minutes. Remove beans and parchment, then bake for another 5 minutes. Reduce the oven temperature to 170C/340F/Gas 3½.
              
              
              
                03 - 
                Mix the zest and juice from the lemons with 2 1/4 oz cornstarch to form a paste. Boil 16 fl oz water and add the lemon-cornstarch mixture, stirring until thickened. In a bowl, whisk 9 oz superfine sugar with 6 egg yolks. Gradually whisk the mixture into the pan and stir over medium heat until it thickens further. Pour into the baked pastry case.
              
              
              
                04 - 
                Whisk egg whites in a stand mixer until soft peaks form. Gradually add superfine sugar, whisking until stiff and glossy. Sprinkle in 2 tsp cornstarch and whisk to incorporate. Spread the meringue over the lemon filling, covering completely, and create swirls with the back of a spoon.
              
              
              
                05 - 
                Bake the pie at 170C/340F/Gas 3½ for about 15 minutes until the meringue is golden and crisp. Let the pie cool completely before slicing, or chill for an hour for cleaner slices.