New York City's Serendipity 3 restaurant has a history of doing stunts to make the Guinness World Records. They've scored twice before -- with the World's Most Expensive Ice Cream Sundae and the World's Largest Hot Chocolate -- and on Friday, they did it again with the World's Most Expensive Hot Dog, which will sell for $69.So how do you get a hot dog to cost nearly 70 bucks? First, you start with a regular Serendipity 3 foot-long beef hot dog, which already sells for $8.50 -- a little more than your average street dog in New York (and a lot tastier, I'll admit). Then you use the tried and true pre-recession stunt of chefs around the world: Add foie gras, then add truffles, repeat as necessary until the price tag explodes. (The other surefire fancifier -- caviar -- would taste a little gross on a hot dog, though Serendipity 3 puts it on a burger.)To be more specific, this particular "Haute Dog" (as it's being marketed) is grilled in white truffle oil and is served on a chewy pretzel-bread bun (sort of like a cross between a soft pretzel and a baguette) that's toasted with white truffle butter. It's topped with foie gras pâté with black truffles. Condiments (served on the side) include Dijon mustard with black truffles, caramelized Vidalia onions and ketchup made with heirloom tomatoes (more like a tart tomato relish).