Place oyster liquor and heavy cream in a 10-inch skillet. Reduce this over medium heat for about 1 minute. Add the oysters, milk, sherry, ½ teaspoon salt and a pinch of pepper. Heat over low heat until the edges of the oysters begin to curl. (Do not overdo this step or the oysters will toughen.) Turn the heat off and swirl the butter into the soup. Blend until it is completely incorporated into the soup; adjust the seasoning.

Ladle the soup into heated soup bowls and dust each one with parsley.