To make the pastry, sift the flour onto a work surface and make a well in the centre. Place the oil, egg and 125 ml (1/2 cup/4 fl oz) lukewarm water in it. Using a flat-bladed knife, start from outer rim and work the flour into the liquid ingredients. Electric beaters can be used, if preferred.
Knead for about 10 minutes to make a smooth dough. Shape into a ball. Heat a bowl and invert it over the dough, leaving it for about 45 minutes. Maintain temperature of the bowl by repeatedly covering it with a warm, damp cloth.
To make the filling, melt all but 1 tbsp of butter in a pan. Add breadcrumbs and fry until golden. Cover sultanas with warm water and let soak for 15 minutes; drain. Peel and core apples; slice thinly. Combine sultanas, apples, almonds, cinnamon, sugar and breadcrumbs in a bowl.
Preheat oven to 200 degrees C. Spread out a clean cloth kitchen towel, sprinkle thickly with flour and place the dough on it. Roll dough out very thinly.
Melt 1 tbsp butter and brush the dough with it. Dust hands with flour and slide them under the pastry into a position that makes it possible to stretch the dough well in all directions. The dough must be stretched so thinly that the pattern of the towel is visible through it.
Spread filling over the pastry, keeping clear of the sides and lower edge. Begin at the narrow end of towel and carefully roll strudel up, using the towel to help. Firmly press the edge and sides together. Leave whole or cut in half.
Grease a baking tray; carefully place strudel on it and bake for 30–40 minutes. Sprinkle with icing sugar while still warm.
Apples supply vitamin C as well as some potassium. It's best to eat the peel to get the full measure of fibre. Some of the fibre in apples is pectin, which is thought to help lower blood cholesterol. It is best to store apples in the refrigerator because they tend to deteriorate quickly at room temperature; the flesh turns mushy and the apples lose some of their vitamin content.