Eel sauce is made with soy sauce, sugar and mirin cooked down together into a glaze. It’s commonly used in Japanese cooking as a condiment for both fresh water and salt water eel and other long, scale-less fish, and can be used in sushi or non-sushi preparations.

Eel sauce is in the Inception stage. It’s considered a premium ingredient that can be found mostly on fine-dining menus and at independent restaurants.

The Mori Eel Hamburger at 26 Beat Restaurant in Venice, Calif., is topped with unagi (fresh-water eel), eel sauce, green onions, avocado, sushi ginger, seaweed, radish sprouts, Boston lettuce, tomato, black sesame seeds and mayonnaise.