French onion soup is a type of soup usually based on meat stock, and often served gratinéed with croutons and cheese on top. Although ancient in origin, the dish underwent a resurgence of popularity in the 1960s in the United States due to a greater interest in French cuisine. French onion soup is usually a plate that is served as a starter. Generally, recipes specify that the onions should be cooked slowly, becoming caramelized.