Pour your chilled sherry into a glass until its three-quarters full.
The reason most fine sherry's (manzanilla or fino) come in half bottles is, in Spain an open bottle is kept no longer than a single day to perserve freshness.
BTW: The so called cooking "sherry" found in the supermarket is not really sherry. It is a cheap American wine heated up to give it a baked, caramel flavor and then salt is added to it.
