Steam the leek in the butter until translucent. Season, let cool and fold in the cheese.
Lay out the strudel dough. Brush with oil and place a second layer of strudel pastry on top. Now spread the filling evenly on. Roll up tightly lengthways and brush with oil or butter.
Close the edge tightly.
Preheat the oven to 180 ° C top / bottom heat. Place the strudel on a baking sheet lined with baking paper and bake for about 15-20 minutes on the middle rack, until the surface is slightly brown.
Cut into strips approx. 2 cm wide and serve in the hot soup.