About this recipe: This classic sauce is best served with fresh fish. Make it just before you need to use it.
*To make a cheese sauce, stir 50 g grated cheese (such as mature Cheddar, Gruyère or Parmesan) into the sauce just before serving. A sprinkling of cayenne pepper or nutmeg or 1 tsp mustard improves the flavour. *Alternatively, use other chopped fresh herbs such as chives or tarragon in place of parsley.