Start this recipe by preparing the crumble. Place the gluten-free flour, ground almonds, 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 flaked almonds. The mixture should resemble a heavy crumble. Place 2/3 of the mixture into a well greased spring form cake tin, pressing the crumble in the bottom and on the sides of the tin tightly. Next, prepare the filling. Heat the butter in a large pan and add in the apples. Cook gently for a few minutes, then add in the sugar and spices and continue to cook for 4 minutes. When the apples are slightly softened, stir in the sultanas, cornflour and water and mix together well. Tip the apple filling into the crumble lined tin and even out. Carefully scatter over the remaining 1/3 of crumble mixture and bake in the oven at 200`c for 30-35 minutes. Remove from the oven and allow to cool down slightly before serving with the pouring custard.