FREE Sin City Burger at Smashburger! Thursday, 9/12 ONLY! Stop by your local Smashburger on Thursday, 9/12 to get a FREE Sin City Burger. The Sin City Burger is made with 100% certified Angus Beef, topped with a fried egg, thick applewood smoked bacon, American cheese, grilled onions, haystack onions and their Smash Sauce on a classic bun. Valid at participating restaurants only One per View Post