You can start this recipe by preparing the date and orange filling. Place all the ingredients except the walnuts in a saucepan, and cook for about 5 minutes on a low heat, till the dates are soft and creamy. Mix well to a nice smooth paste then mix in the chopped walnuts and mincemeat and put aside to cool. Next prepare the sweet pastry. Sift the flours into a large bowl and add the butter. Rub the ingredients together with your fingertips until the mixture resembles breadcrumbs. Add in the icing sugar, orange juice and zest, vanilla essence and the egg yolks and mix together to form a smooth pastry (alternatively you can prepare the pastry in a food processor). Wrap the sweet pastry in cling film and chill for 30 minutes in the fridge. When the pastry has chilled and firmed up, remove it from the fridge and discard the cling film. Roll out the sweet pastry using a rolling pin on a lightly floured surface to a thickness of 5mm and use to line the base and sides of a 24cm fluted flan tin. Press into the corners and trim off any excess pastry. Spoon over the delicious filling and even out with the back of a spoon. Use the trimmings to cut out strips and place decoratively on top of the filling to form a lattice design. Brush the surface with a little beaten egg and back in the oven at 180`c for 30-35 minutes, or until golden brown. Remove from the oven and allow to cool in the tin before dusting with icing sugar. Can be served whilst still warm or cold.