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Whilst egg sandwich history started before this, during World War II and prompted by meat rations, a manager for a White Castle at St. Louis introduced the first fast food egg dish with a fried egg sandwich. However, the dish was unpopular, and was abandoned as soon as the meat rations were lifted.
Beyond the basic model of fried egg between slices of bread, many common sandwiches have variations that include a fried egg in addition to bacon, sausage, cheese, black pudding, cold cuts, or as another topping to a hamburger. A popular breakfast sandwich in New Jersey consists of a fried egg, pork roll, and American cheese on a roll, often topped with salt, pepper, and ketchup. The Southern egg sandwich consists of bread, egg, cheese, and mayonnaise. A savory/sweet variation from California is the Lawler Sandwich; it is made of a fried egg (broken yolk), bread, cheese, mayonnaise, and jam (typically raspberry).
A popular filling snack with British troops since at least World War I, the "egg banjo" is a sandwich of a runny fried egg between two thick slices of bread (if possible, buttered or with margarine), often accompanied by a mug of "gunfire". A popular account of the term's origins, possibly a false etymology, is the act of cleaning spilt egg off one's body, the sandwich held out to the side with one hand whilst the other wipes at the drips, giving the impression of playing an invisible banjo.
Egg banjos are still quite common in certain Commonwealth countries. For example, sold by roadside burger vendors or, in Malaysia, as street food.
A 1905 British cookbook describes an "egg sandwich" made with sliced hard-boiled eggs, marinated in oil, vinegar, salt, and pepper, and garnished with minced watercress. An "egg and chutney sandwich" is made from chutney and minced hard-boiled eggs; an "egg cream" sandwich from hard-boiled eggs pounded into a smooth paste and seasoned with anchovies and mustard. A common alternative is to mash the hard-boiled egg together with mayonnaise, salt and black pepper, usually called simply egg spread, or an egg mayonnaise or egg mayo. Cress is often seen as the typical accompaniment to an egg sandwich.
It is worth noting in passing that the term sandwich in British or Australian use always refers to a filling of any sort between two slices of bread: that is, bread slices from a loaf. An egg sandwich is thus egg between two bread slices. The same filling served in a cut roll, bagel, muffin or the like is not, ever, a "sandwich". It is an egg roll, egg bagel, egg muffin etc.
Banjo noun 1 a generously proportioned sandwich or filled roll. In military use in forms such as an "egg banjo" or a "chip banjo".