Add 1 tablespoon of olive oil to a large skillet over medium high heat then add onions, tossing for 2 minutes. Lower heat to medium and continue to cook for 15–18 more minutes until the onions are very soft, but not burned. Stir in 1 tablespoon of Momofuku Black Truffle Chili Crunch.
Combine ground beef, Momofuku Soy Sauce, Momofuku Savory Seasoned Salt, and Momofuku Black Truffle Chili Crunch in a large bowl and mix until well combined. Shape into two large patties with a large divot in the middle. (They will level out in cooking.)
Heat skillet over high heat until hot, then add burgers. Cook for 4 minutes undisturbed, then flip, top with cheese, and cover. Cook for 2 more minutes or until desired doneness.
To serve, spoon 1 tablespoon of dijon mustard onto the bottom of each of the buns, top with burger, then layer on a generous portion of the caramelized onions.
