Sauce Verte de Chausey

The granite islands of Chausey are off Granville. Whether this sauce was made there, I have not been able to discover. Perhaps it was named for its dark, speckled-green colour, rather the effect of granite. The mustard makes it a good sauce for gurnard, garfish, herring, mackerel, saithe or huss. If you cut down the mustard, or increase the cream and butter, it goes well with salmon.