Shake Shack Inc. closed its second day of public trading on the New York Stock Exchange at about 120 percent higher than its IPO. Photo courtesy Shake Shack

NEW YORK, Jan. 31 (UPI) -- Manhattan-based burger chain Shake Shack shook up the stock market in a public debut that closed at $45.90 on Friday, nearly 120 percent higher than its IPO price of $21 the day before.

Shares of the company, which trade under the SHAK symbol, more than doubled in the first full day of trading, hitting a high of $52.50. Shake Shack founder Danny Meyer saw his 21 percent stake in the company rise to $342 million.


"Nothing has surprised us more than a hot dog cart we started 14 years ago that became Shake Shack," Randy Garutti, the company's chief executive, told The New York Times.

Shake Shack started out of a New York City hot dog stand in 2001 and currently operates 63 restaurants, with outposts in London, Moscow and Turkey. There are plants to build more around the United States.

Reveling from the success on Friday, Shake Shack dished out free burgers served out of trucks near Wall Street. Shake Shack calls itself "fine casual," capitalizing on offering premium burgers and high-level hospitality.

Part of that comes from paying many of its employees more than the local minimum wage.

"We believe that this enables us to attract a higher caliber employee and this translates directly to better guest service," the company said.

Line 'em up: we're serving free Shack 'til 2pm outside the New York SHACK Exchange @nyse pic.twitter.com/E7ltchuzLA — SHAKE SHACK (@shakeshack) January 30, 2015