Sieve the flour into a bowl, add the other ingredients and knead it all into a smooth dough. Brush the dough with oil, put it back in the bowl, cover that with cling film and let it rest for at least 30 minutes (the longer, the more elastic the dough gets).
If you use fresh apples, peel and core them and cut them into thin slices. Put them in a bowl and mix them with lemon juice to prevent them from browning. If you use dry-canned apples, just put them into the bowl.
Roast the nuts in a pan without fat until they are lightly brown. Immediately get them out of the pan and either grind them finely in a kitchen mixer or put them as they are (as chops or flakes) to the apples.
Add the raisins (if you like), sugar and cinnamon and mix it all well.
Dust a kitchen towel with some flour and roll out the strudel dough on it with a rolling pin. Now pull the dough with your hands to the desired size.
Spread the filling evenly across the whole dough but leave out about 2 cm (1 inch) from the edges.
Fold the shorter edges in and roll the strudel with the help of the kitchen towel. Put the strudel either on a baking tray or in a roasting pan that is either covered with a baking tray or greased with butter, lard or tallow.
Brush the strudel with butter and egg yolk and bake it in the preheated oven for 45 minutes at 180 °C (350 °F) (no fan-oven).