The story goes that a woman in Dallas TX was eating lunch at a Neiman-Marcus café, and decided to try the “Neiman-Marcus Cookie”. It was so good she asked for the recipe, and when they wouldn't give it to her she offered to buy it. They said the price was “two-fifty,” which she thought meant $2.50, and when the $250 charge hit her credit card she realized the misunderstanding. She called the company to ask them to reverse the charge, but since she already had the recipe, they refused. In retribution, she decided to make the recipe public, and get her money's worth.
The story is completely false; it never happened. Neiman-Marcus has developed their own real cookie recipe which they make available on their web site for free. However, the recipe attached to the urban legend is quite good! Nobody knows where it really came from, but here it is (with a slight improvement by yours truly).