Scald the oysters in their own liquor. Drain and mince, but not too fine. Put into the saucepan a tablespoonful of butter, and, when melted, add the parsley (chopped fine), the herbs and the mushrooms. Then add the flour, which has been rubbed smoothly in a gill of Oyster liquor, and, after it stews about five minutes add the White Wine; if this is not obtainable, add another gill of Oyster liquor. Mix thoroughly, and then add the minced Oysters, and stew gently until the sauce is absorbed and the mince forms a thick batter. Be very careful not to scorch. Remove from the fire and add egg yolks which have been beaten smoothly in the cream. Set it back on the fire and let it remain about one minute, then serve on large toasted and buttered Croutons, with a garnish of lemon, parsley and olives.