Happy National Cheeseburger Day! In honor of the holiday, we went to the holy grail of New York burger spots, Shake Shack, to get the lowdown on their famous creations. Zach Koff, their VP of operations, was on hand to explain what's so exceptional about Shake Shack's three biggest-selling burgers. And we had to ask: what is in that special sauce?Subscribe to POPSUGAR Food!http://www.youtube.com/subscription_center?src_vid=wNSZWHtiGek&add_user=popsugartvyumVisit our website for more easy recipes and cooking tips!http://www.yumsugar.comAre we friends yet? Join us on Facebook!https://www.facebook.com/POPSUGARFoodGet the latest updates via Twitter!https://twitter.com/#!/POPSUGARFood
