Knead 250 g flour, 1 pinch of salt, egg, 2 tablespoons of oil and approx. 100 ml lukewarm water with the dough hooks of the mixer to a smooth dough. Then knead vigorously with your hands for about 5 minutes, hitting the work surface several times. During the dough tension test the dough must stretch without tearing immediately.
Shape the dough into a ball, brush with oil, cover and let rest for about 30 minutes. While the dough is resting, preheat the oven (electric oven: 200 °C/circulating air: 180 °C/gas: see manufacturer).
Roll out the dough on a floured work surface to about half the size of a tea towel (approx. 47 x 50 cm).
Dust the tea towel with flour. Pick up the dough and pull it out thinly all around with floured backs of your hands (in the size of the cloth).
For the filling, chop 100 g hazelnut kernels, roast them in a pan without fat and take them out. Melt 50 g butter in the hot pan and roast 100 g breadcrumbs in it while stirring. Stir in 100 g sugar and 1 teaspoon cinnamon, take out. Peel 1 kg sour apples (e.g. Boskop), quarter, core and cut into slices. Mix in 2 tbsp. lemon curd and nuts.
Next step: The merger! For this, melt 75 g butter in a pot, spread the dough thinly with butter. Spread crumbs and apple mixture one after the other on one half of the dough, leaving about 1.5 cm of edge free.
Wrap the sides over the filling and roll up loosely from the shorter side using the cloth, then place on a baking tray lined with baking paper. Remove the cloth, making sure that the end is at the bottom.
Brush the strudel with some butter and bake for about 35 minutes. Remove, immediately brush with remaining butter and let cool for about 30 minutes. Dust with some icing sugar.