Cut the meat into strips. Cut the white and light green parts of the leek into rings. Finely chop the onion. Heat the oil and fry the meat vigorously. Add the leek and onions and fry for a few minutes.
Season with salt and pepper, pour in the soup and simmer covered for about 30 minutes. Mix the cornflour with a little cream. Pour the remaining cream into the sliced meat, bring to the boil and thicken with the mixed cornflour. Stir in the parsley and season to taste.