There is a difference between strudels depending on where they come from. This is a typical basic pastry recipe for a Hungarian strudel that can be filled with hundreds of different sweet or savoury fillings. Apple, sweet ricotta, cherry, poppy seed paste are the most popular ones, you will see in patisseries. If you are lucky to have tried some home made rétes at your or some friends grandparents house then you may be familiar with some savoury fillings such as cabbage, potatoes and sausage or pumpkin. These strudels don't have the lettuce-work pastry topping like the Viennese strudels, so don't mix them up.
The success of a good strudel pastry depends on the flour, which has to have a high protein content. If you use plain flour, some recipes recommend adding an egg to it just to raise the overall protein content. I have not tried this yet, but searched through all the flours in the supermarket, and found the very strong bread flour had the highest gluten content of all. This gives the pastry its elasticity so it is easy to stretch so thin that you can read a book through it. Apparently. Kneading it by hand for a good 20 minutes also helps developing the right texture. I wouldn't say my kneading was of an experienced rétes-maker, hence the layers were less impressive when it came out of the oven. More practise definitely needed! (There are excellent tutorials for stretching strudel pastry on Youtube if you can't picture how to do it).
Of course you could use ready made filo sheets, but these are usually far too small and taste a bit like baking parchment - nothing like the real thing! Also traditionally, fat would be used instead of butter, but this really wouldn't be very popular here in the UK so I adapted the recipe.
For the pastry:
500g flour (with highest gluten content)
40g butter (and more for brushing the pastry before filling)
400ml warm water (mixed with a pinch of salt and tsp vinegar)
For the filling (which I would start cooking before starting on the pastry):
1kg dessert apples
200g granulated sugar
handful of sultanas
Cinnamon stick or tsp of ground cinnamon
Make the filling first so it has time to cool. Peel, core and grate the apples. Place in a heavy bottom pan with the sugar, cinnamon, sultanas and cook until soft, almost creamy texture and most of the juices have evaporated. Cool completely before filling the pastry.
Crumble the butter into the flour between your fingers or use a food processor for this, as if you were making a crumble topping. I guess mixing by hand is more traditional and may contribute to perfect strudel stretchiness... When all mixed and smooth, start adding the water until you have a soft dough. You need to knead this, softly stretching it and knocking it back for about 20 minutes by which time you should have a soft, elastic dough. Divide this in two (for two strudels) and cover them with a warm dish (I stuck a couple of pans in the oven to warm up while kneading the dough). Leave to rest for another 20 minutes. Preheat the oven to 180C.
Cover your dining table with a clean tablecloth and dust with flour. Start by rolling the first dough out as much as you can with a rolling pin then carefully start stretching it with the back of your hand. Stretch it as much as you possibly can but do not despair if you cannot read a book through it. You may have a few minor holes in the pastry but by the time you roll it up it will all disappear and look perfect.
Let it dry for a few minutes then brush generously with melted butter. Sprinkle with semolina or breadcrumbs under the filling to stop the pastry going soggy. Spread half the filling at one end of the pastry in a line and with the help of the tablecloth start rolling it up. It should be flat rather than a round roll shape. Once rolled you could cut the pastry edges clean off the end and sides if you need to. Place on a lined baking sheet and make the second strudel. When both strudels are ready, brush with a beaten egg and bake in the oven for 30-35 minutes or until golden and the pastry layers are cooked through. Slice, dust with icing sugar and serve warm.