Trim the watercress, removing any tough stems.
Place in a saucepan with a little water and bring to the boil.
Simmer for 5-8 minutes.
Drain well and chop finely, using the double-bladed chopping knife.
Bring the cream to the boil and stir in the finely chopped watercress.
Season to taste and add a few drops of lemon juice.