This section is from the book "The Art Of Naming Dishes On Bills Of Fare", by L. Schumacher. Also available from Amazon: The Art of Naming Dishes on Bills of Fare.
Kegarding the writing of singular or plural on menus and bills of fare the following should be kept in mind.
Such items and pieces of food of which a guest may have only one for a certain price, •must be marked in the singular, for instance: beefsteak, cutlet, herring, apple, pear, etc. All large pieces of which a guest may have only a part, are also written in the singular as for instance: roastbeef, salmon, chicken, leg of mutton, etc. Fruits and other dishes which are standing on the table for ones free choice can be marked in the plural. All other dishes of which the guests may have more than one, such as: eggs, oysters, plums, crabs, anchovies, etc., should be marked in the plural.
On menus and bills of fare without quotations such dishes as herrings, beefsteaks, cutlets, etc., can be marked in the plural because guests can order more than one of an item. But this is not a rule and writing it in the singular is just as correct.