According to Guinness World Records, the most expensive hamburger can be found at Serendipity 3 in NYC:
The hamburger is made from white truffle butter-infused Japanese Wagyu beef and topped with James Montgomery cheddar cheese, black truffles and a fried quail egg. It is served on a gold-dusted campagna roll spread with white truffle butter. The roll is topped with a blini, creme fraiche and caviar.
I love food made with gold; makes your poop all glittery.