Place flour, salt, egg, vinegar, oil, butter and water in a large bowl; knead with the dough hooks of an electric mixer for 5 minutes, or by hand. Cover the dough and leave it to rest for 30 minutes.
For the filling, fry the bacon in a large pan. Chop the sauerkraut, add it to the bacon and season with caraway seeds. Pour in the stock, cover and braise the cabbage over low heat for 10 minutes. Season with salt and pepper; drain in a sieve.
Preheat oven to 220°C and grease a large baking dish. Place an ovenproof dish of hot water on the floor of the oven.
Knead the dough briefly on a lightly floured work surface. Divide the dough into 4 portions; brush with melted butter. Roll out each portion on a lightly floured cloth towel and, using the backs of your hands, stretch the dough into paper-thin rectangles.
Brush the dough sheets with melted butter. Spread the filling over the sheets, keeping the side and back edges clean. Moisten edges with stock.
Roll up the strudel using the cloth to help. Slice each roll into pieces about 6 cm wide. Place the pieces a little apart in baking dish. Brush with remaining melted butter. Bake for 40 minutes, basting with stock or white wine every 10 minutes, until the pastry is golden brown. Serve hot.