Put the oysters and their liquor, butter, and half-and-half in a nonreactive sauté pan. Bring rapidly up to a near boil and immediately turn off the heat. As soon as the oysters plump up (about 30 seconds), puree the oysters and cream. Taste for salt, reheat, and pour into warmed bowls. Put a spoonful of caviar in the center of each portion of soup.