In the bowl of a food processor, combine the flour, butter, salt and sugar until the mixture resembles breadcrumbs. With the motor running add the beaten egg and continue processing until the mixture forms a ball. Form a disk, wrap in plastic and refrigerate for 2 hours. Preheat the oven to 350 F. Roll out the dough on a lightly floured surface to a 1/4 inch thick. Line a 9 or 10-inch tart pan with the dough and prick the base with a fork. Place a piece of foil or parchment paper over the dough and fill with rice or dried beans. Bake for 20 minutes, until golden brown. To make the filling, put 3/4 cup of the sugar, the egg yolks and lemon juice in the top of a double boiler and whisk constantly until the mixture becomes very thick. Remove bowl from heat and leave to cool. Beat the egg whites to the soft peak stage, then beat in 1/4 cup of the sugar 1 tablespoon at a time until stiff. Fold the egg whites into the lemon cream. Whip the cream with the confectioner╒s sugar until very thick. Fold the whipped ceam into the lemon cream and fill the cooled pie crust with this mixture. Place the remaining sugar in a medium saucepan with a cup of water and stir over a low heat until the sugar dissolves. Once the sugar dissolves raise the temperature and boil for 5 minutes. Add the lemon slices to the sugar syrup and simmer for 2 minutes. Drain. Arrange the lemon slices on top of the tart.
