A lardon is a cube of meat which is usually high in fat and used to add flavor to many dishes. Generally, bacon is used to make lardons, but general pork lardons are also common. When cooked, a lardon will reduce in size as a result of the fat melting out of it. The juice that comes out of lardons is used for additional flavor in dishes such as coq au vin and some stews. Originally, lardons were pushed into cuts of meat so that they would flavor the entire cut with their fat.
Either smoked or un-smoked bacon can be chopped up into lardons. Any fatty cube of meat can be classed as a lardon, but generally pork fat is used. The saltiness from the fat and the meat itself is what adds flavor to whatever dishes are created. The French refer to any bacon that has been cut into cubes before being blanched or fried as a lardon. In the wider world, lardons are bought pre-cut, but cubed bacon can be used in their place, in line with the French usage of the term.
Originally, a lardon was more of a matchstick-shaped strip of meat which was stuffed into a bigger cut of meat to add flavor. This process is referred to as larding, and can be thought of as essentially adding more fat, or “lard,” to a cut of meat. The original concept of lardons is now somewhat secondary to the more modern use of cubes instead of strips. Lardon cubes are ordinarily used as a base flavor for dishes.
When fat is heated, it transforms from its original solidified form into a liquid. This liquid bears all of the taste of the original fat, but can be added to sauces much more easily. A lardon adds flavor to a dish because of this reaction. Chefs who cook with lardons will generally shallow-fry them along with onions before adding chopped tomatoes or another sauce base. The fat seeps out and adds a salty, robust flavor to the sauce.
Many dishes can be improved by using a lardon or several lardons. For example, a sausage and bacon stew can be made which uses lardons as a base flavor. The lardons are fried in olive oil until they have shrunk and turned golden brown, at which point garlic and other flavors are added. Lardons can also be used in dishes such as quiches, salads, and pasta sauces.