First knead the dough from the flour, sour water and a pinch of salt. Roll out a rectangular shape from the dough and coat it with half of the butter or margarine. Roll out the dough by forming a cube and leave it in the freezer for 20 minutes to harden. Roll out the dough into a rectangular shape 1 cm thick. Apply the other half of the margarine or butter and fold the dough back into a cube. Leave for 20 minutes in the freezer to rest. Roll out the dough into a thin rectangular shape (about half a cm) and divide it into two equal parts. Coat both parts with the prepared mixture by mixing the mustard and sour cream together in a deep bowl. Arrange pieces of bacon on the coated part. On the crust where the bacon is arranged, fold in the crust that is coated only with the mustard and sour cream spread. Using a knife, cut long strips and fold them several times, coat them with beaten egg and sprinkle with sesame seeds. Bake in a preheated oven at 180 degrees for about 20-25 minutes.