Mix together the flour, butter, icing sugar and water. Press the soft dough into the base and up the sides of a 20cm (8inch) fluted flan ring. Pierce the base several times and bake blind on a baking tray in a preheated oven 190?C/375F/Gas Mark 5 for 20 minutes, until golden. Reduce the oven temperature to 150?C/300F/Gas Mark 2. Place the caster sugar, eggs, cream and lemon rind and juice in a bowl. Whisk together until blended, then carefully pour into the cooked pastry case. Return to the oven and cook for a further 35-40 minutes, until set. Arrange lemon slices on top, sprinkle generously with icing sugar and place under a preheated grill for 2-3 minutes until golden. Sprinkle with grated lemon rind and serve with creme fraiche or cream. NOTES : Delicious citrous tart, serve with creme fraiche.