Peel and chop apples. Place in a non stick saucepan. Add sultanas and a splash of water. Simmer till apples are soft, then stir in vanilla. Remove from heat and set aside.
Cream together the butter and sugar till light and creamy, then beat in one egg at a time. Stir in the flour by hand, along with any spices. Finally, fold in the cooled apple mixture. Tip into a greased square cake tin, about 20cm. Sprinkle the top with demerara sugar.
Place into a preheated 160 C / Gas 3 oven and bake for 50 to 60 minutes, or till a knife inserted in the centre comes out clean. Let cool in tin before slicing.