Preheat the oven to 180 C / Gas 4. Lightly grease and flour a 23cm tart tin.
In a bowl, sift flour and cornflour; transfer to the bowl of a food processor. Add sugar, butter and egg yolks; process until the mixture comes together in a ball. Wrap the pastry in cling film and chill it in the fridge for 20 minutes.
Arrange pastry in prepared tart tin; prick with a fork. Bake for 20 minutes in preheated oven. Let the pastry case cool slightly in the tin, then transfer to a dessert plate.
Lemon mousse filling:
Place lemon juice and condensed milk in a bowl. In another bowl, beat the cream until it is thickened but not whipped; form cream in gently to the lemon mixture. Add the gelatine and stir well.
In a clean, dry bowl, beat the egg whites until stiff; fold into the lemon mixture. Pour the lemon mixture into the cooled pastry case and refrigerate for at least 30 minutes.
Arrange fruit in a pretty design on top about 30 minutes before serving to prevent the juice leaking too much. Dust with icing sugar if you like.