Bisque de cribiches (freshwater crayfish bisque)

4 tb butter, unsalted
      2 lb Crayfish; cleaned, shelled
      1    Onions; chopped fine
      2    garlic cloves; chopped
      1    Fennel sprig; (optional)
      1 sm Pepper, hot; left whole
      4 c  Water
      1 c  Milk, coconut
      2    Egg yolks
           Salt; to taste
 
    Heat butter in heavy saucepan and add crayfish, onion and garlic. Saute
  over medium heat until the crayfish have changed color, about 5 minutes.
  Add the fennel, hot pepper and water. Cover and cook at a gentle simmer
  for 30 minutes. Remove and discard the fennel and the hot pepper. Remove
  the crayfish and pound in a mortar and push through a fine sieve or reduce
  to a puree in an electric blender with a little of the stock.
    Return the pureed crayfish to the saucepan, add the coconut milk and
  heat through. Beat the eggs yolks with a little of the soup and stir into
  the saucepan. Cook over low heat, stirring constantly, until the soup is
  lightly thickened.
    The crayfish shells may be simmered the water first to make a more
  flavorful stock instead of using plain water.