Preparation

Sieve the flour onto a board, make a hole in the middle of it and add the oil into the hole. Gradually create a paste by adding water into which you put salt and vinegar. Then continue to knead for 10 minutes until smooth. Divide it into four parts, knead and round them, put on a board sprinkled with flour, coat with oil and cover with a larger bowl. Let the dough rest for 30 minutes.

Heat up the milk in a pan, pour it over the poppy filling and allow it to cool. Put the squash in a bowl, season with salt and let sit for 30 minutes to release the liquid out soften the squash. Then drain and squeeze the excess liquid with your hands. Mix the poppy filling mix with sour cream, add the drained squash and mix it all well together.

Roll the pastry with a roller on board, brush with oil, and then slightly stretch  it with the upper parts of the hand into a circle. Put it on the table cloth and stretch with your hands (not fingers) until it becomes thin and transparent. Cut thick edges and sprinkle the surface of the pastry with 2-3 tablespoons of oil.

Arrange a quarter of the filling onto the dough, but not all the way to the edges of the pastry. On three sides, fold the edges of the pastry and start rolling the dough a bit wider on the side where the filling is. Place a strudel in a greased baking pan and repeat the process with the rest of the pastry and filling.

Coat the strudel with a mixture of sour cream and egg and bake in a preheated oven at 180°C (350°F) for about 40 minutes.