To take advantage of the offer, simply mention of the promotion to your cashier when ordering in-restaurant, or use promo code “15YEARS” when ordering online or via the brand’s mobile app.

The Cheesy Caramelized Onion Smash features a Certified Angus Beef patty, topped with melted cheddar cheese, aged Swiss cheese, caramelized onions, tomatoes, lettuce, and mayo, all on a toasted onion bun.

In addition to being customizab…