The sauce requires no cooking and can be made in minutes using a food processor or blender. Use two bunches of watercress for a more pronounced flavour. In summer the sauce is ideal for serving with cold chicken, or fish, such as salmon or trout. To serve it hot, warm it gently but don't allow it to come to the boil as it will curdle.

1. Wash the watercress and chop off the base of the stalks.
   
   
   
   
2. Put the watercress into a food processor and chop finely. Add the soured cream and process for a little longer until well blended and light green in colour.
   
   
   
   
3. Add a squeeze of lemon juice to the sauce and season to taste with salt and pepper, before blending for a few more seconds.

Tip: To make a dip to serve with crudités, prepare the sauce with two or three bunches of watercress. Add the soured cream in stages until the consistency is right—it should be a little thicker than when making a sauce.