A Bacon, Lettuce and Tomato (B.L.T.) is a popular type of sandwich in the United States, the U.K., and other parts of the world. Simple in construction and ingredients, it traditionally consists of five ingredients; bread, bacon, lettuce, tomato and mayonnaise. Many varieties exist, mostly simple variation of the five ingredients or the addition or omission of the same.
- Bread: Traditionally lightly toasted white, sliced bread (2 slices). A three-bread-slice version with turkey is better known as a club sandwich. Wheat and rye breads are also popular. In Puerto Rico, criollo-style bread or "sobao"-style bread may be used instead, sometimes adding pickles.
- Bacon: The "B" on the BLT, its presence is not debatable; no bacon means no BLT. The popularity of bacon substitutes (turkey bacon, meatless bacon substitute) allows some people to delude themselves that they are eating a "turkey BLT" or a "meatless BLT", when in reality these are mere pale imitations of the original. Traditionally, the bacon is crisp, though these days it is more of a matter of taste, the only real difference being the amount of bacon added; 2, 4 and 6 slices are common, while some places specialize in adding bacon by the half or full pound. In any case, the Bacon should NOT be hot enough to wilt the lettuce or tomato.
- Lettuce: Despite the belief of some newscasters, Lettuce is a non-negotiable ingredient in a BLT: it is the "L" in BLT, without Lettuce, it is just a bacon and tomato sandwich. Leafy varieties are best, though it is a matter of personal preference. Traditionally, iceberg has been used for its crunch, though Romaine is also popular for its colour and flavour. Some leeway may be made with substitutes, such as celery leaf or fresh spinach, but these tend to be variants instead of true BLTs.
- Tomato: The main substance by weight, the "T" of the BLT is also not negotiable. Generally several thin slices or 1-2 thick slices are used to add weight and substance to the sandwich, as well as contrasting texture to the crisp saltiness of the bacon and the cool crunch of the lettuce. Using ketchup, marinara sauce, tomato paste or Mexican-style salsa is NOT an acceptable substitute for fresh, sliced tomatoes.
- Mayonnaise: though not "lettered" in the BLT title, most connoisseurs would balk at calling a sandwich a BLT if it did not have mayonnaise or an acceptable substitute such as Miracle Whip, Baconnaise, Dijonnaise or (arguably) sandwich spread or creamy-style salad dressing. The spread is often used as a barrier between the bread and lettuce in order to prevent the moisture in the lettuce and tomato from making the bread soggy.