Rub the butter into the flour and icing sugar until it resembles breadcrumbs.
Stir in the beaten egg and bring together to form a dough.
Chill the dough for 30 minutes, roll it out, and line a 28cm tin.
Preheat the oven to 200°C.
Beat the eggs, caster sugar, lemon rind, and juice together.
Stir in the warm melted butter.
Grate the Bramley apples into the mixture and mix well.
Spread the lemon mixture over the chilled pastry base.
Level the surface and arrange the dessert apple slices on top.
Sprinkle the demerara sugar over the surface.
Bake on a heavy tray for 40 to 50 minutes until firm.
Serve warm or cold.