For the dough, sift flour into a large baking bowl, pressing a bulge into it. Pour in water, salt, vinegar and 2 tbsp. oil and stir to form a thick paste. Knead with the remaining flour from the edge until smooth, shape into a ball, brush with the remaining oil and rest in a warm place for about an hour.
For the filling, peel the apples, cut them into quarters, remove the core and cut them into thin slices, sprinkle with the juice of one lemon and mix with currants and chopped nuts.
Roll out the dough on a floured dish and flatten it over the back of your hand until it becomes translucent. Brush with melted light butter or butter, spread sour cream on top and sprinkle with bread crumbs. Spread apple mixture evenly over dough and sprinkle evenly with sugar and cinnamon to taste. Fold edges free and up over apple filling. Roll up the strudel and place seam side down on a greased baking sheet or pan. Brush the strudel with melted fat and bake in the oven at 180 °C for about 45 minutes, basting occasionally with liquid fat.
After baking, serve sprinkled with powdered sugar. Serve with whipped cream and/or vanilla sauce and/or vanilla ice cream as desired.