Clean, wash and cut the leek into 4 pieces. Steam in little boiling salted water for 5-6 minutes. Drain. Fry the leek in hot oil, season and wrap the sausage around it.
Place in the pan and sprinkle with cheese. Cover and let it melt. Bring 100 ml water to the boil, add milk and stir in the purée. Season and stir again.