A deep-fried sandwich is any combination of ingredients enclosed by slices of bread, rolls or batter before being submerged in oil and cooked until crisp on the outside and warm on the inside. Most combinations include some type of cheese that melts while the sandwich is cooking in the oil. Other deep-fried sandwich recipes use sweet ingredients such as peanut butter and jelly or fruits. One of the most recognized types of deep-fried sandwich is known as a Monte Cristo, which is made from turkey, ham and cheese between two slices of bread that are battered and then deep-fried until golden brown. Nearly any type of sandwich can be deep-fried, so long as some care is taken to ensure that the contents of the sandwich do not run out into the oil and burn.
There is a distinction made between a deep-fried sandwich and one that has simply been fried in shallow oil. A true deep-fried sandwich is completely submerged in hot oil so it cooks evenly from all sides simultaneously. A sandwich that is only fried in a thin layer of oil or fat tends to crisp only on the bottom, and a smaller amount of heat reaches the contents of the sandwich. The type of oil used for a deep-fried sandwich also is sometimes different from what is used for pan frying, because the deep-frying oil needs to maintain a hotter temperature for a longer time, making it difficult or impossible to used flavored fats such as butter.
One challenge that sometimes arises when making a deep-fried sandwich is maintaining the integrity of the sandwich itself. If simply dropped in oil, all the separate elements would come apart and cook individually. A method that often is used in sandwiches is to dip the sandwich into batter before it is placed into the oil. The batter can quickly form a protective layer on the outside of the sandwich that will allow it to cook on the inside without losing the contents to the oil.
There are a number of savory deep-fried sandwich combinations, including ham, turkey or roast beef paired with a cheese, such as Swiss or Gruyere, which will melt easily from the heat of the oil. These sandwiches also can have ingredients such as tomatoes, pickles or onions inside. Just as popular, however, are sandwiches that have sweet fillings. These may have fruit, peanut butter and jelly, marshmallows, hazelnut spread or candy on the inside. The heat from the oil often causes the different ingredients to melt slightly and form a homogenous filling inside the crisp bread.