a street vendor. In 1974, in an interview with The New York Times, he recounted how he created a hamburger steak sandwich with small strips of beef for a restaurant known as Louis' Lunch. Lassen's family claims 1900 as the year of his invention. Revealed in a public confrontation between the grandson of Louis, Kenneth Davis Lassen Fletch, and his uncle, documentation signed under notary in 1900 demonstrates the development of the hamburger, as it stresses the difference between a "hamburger steak" and a "hamburger sandwich". Louis' Lunch flame broils the hamburgers in the original vertical cast iron gas stoves manufactured by the Bridge and Beach, Co., St. Louis, Missouri, in 1898. The stoves use hinged steel wire gridirons to hold the hamburgers in place while they cook simultaneously on both sides. The gridirons were made by Luigi Pieragostini and patented in 1938. Ingredients Hamburg steak, once served between two slices of bread, began to be prepared with a variety of different ingredients that were included either in the sandwich itself or as a side dish accompanying it on a plate. One of these accompaniments, which is still common with today's burger, is ketchup, a type of tomato sauce with a blend of flavors between sweet and sour that was first produced commercially in 1869 by entrepreneur and chef Henry John Heinz in Sharpsburg, Pennsylvania. His company was originally called the Anchor Pickle and Vinegar Works, but in 1888 it was renamed F. & J. Heinz. The use of ketchup by American consumers grew quickly after this date, and it was not long before hamburgers were almost universally accompanied by ketchup by the end of the nineteenth and into the early 20th century. Mustard is a significantly older condiment, as it is thought that the ancient Romans used a dressing made with non-fermented grapes and grape seeds known as "mustum ardens". Another ingredient incorporated into the burger, mayonnaise, appears to have been present in 18th century France, after the naval victory of Louis-François-Armand du Plessis de Richelieu in the port of Mahón in Menorca around 1756. Among the vegetables that come with the hamburger, the first described in the literature on its history is the onion, usually finely sliced in rings. Thus, the hamburger came to continue the long American tradition of sandwiches featuring some kind of plant product, whether that be lettuce (as in the case of the BLT