It started out as a hot dog cart inside Madison Square Park in 2001 , and its popularity steadily grew .
Shake Shack ( NYSE : SHAK ) is an American fast casual restaurant chain based in New York City .
Shake Shack started out as a hot dog cart inside Madison Square Park in 2001 , and Shake Shack 's popularity steadily grew .
Shake Shack ( NYSE : SHAK ) is an American fast casual restaurant chain based in New York City .