Start this recipe by preparing the pastry. Place the flour, baking powder, butter and caster sugar into a large bowl and rub together till the mixture resembles breadcrumbs. Stir in the lemon zest, vanilla, beaten egg and mix to a pastry. Allow to sit for 15 minutes before rolling out half of the pastry into a circle and use to line the base and sides of a 24cm spring-bottomed tin. Brush the edges with a little water. Next, prepare the filling. Heat the butter and sugar in a large pan and add in the apples. Cook gently for a few minutes, then add in the spices and continue to cook for 4 minutes. When the apples are slightly softened, stir in the corn flour and mix together well. Finally, stir in the Bramley apple sauce. Tip the apple filling into the pastry base and even out. Roll out the remaining pastry and use to cover the apple pie. Trim of any excess and decoratively pinch the edges together. Bake in the oven at 200`c for 30-35 minutes. Remove from the oven and allow to cool down slightly before serving. 5 minutes before serving the apple pie prepare the custard by heating together the milk and vanilla in saucepan till almost boiling point. In a large bowl, whisk together the egg yolks, sugar and corn flour and quickly whisk in the hot milk. Transfer to the pan gain and bring to the boil whisking constantly till the mixture begins to boil. Remove off the heat, pour into a jug and serve with the hot apple pie.