Feb. 5, 2013 -- The youngest female billionaire in the U.S. -- and one of the youngest on Earth -- owes her $1.1 billion fortune to flipping burgers, according to the Bloomberg Billionaires Index.

Lynsi Torres, 30, is owner and president of the In-N-Out Burger chain, whose restaurants have earned a following so devoted, says Bloomberg, that customers line up hours in advance of a new store's opening.

The chain's fans include fellow billionaire Warren Buffett, who, according to a story on the UCLA Anderson School of Business website, told a group of Anderson students in 2005 that he'd like to own the chain.

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Torres didn't found In-N-Out; her family did. According to the company's website, Harry Snyder, Lynsi's grandfather, introduced California's first drive-through hamburger stand in 1948 in Baldwin Park. His wife Esther handled the accounting. From the get-go, the chain emphasized its use of only high-quality ingredients. Burgers today are still made one at a time and always to order, according to the company. Lynsi became president in 2010.

Bloomberg says In-N-Out has grown to include nearly 280 stores in 5 states, with 2012 sales of about $625 million. Bloomberg bases its $1.1 billion valuation for In-N-Out on the metrics of five publicly-traded peers, including McDonald's Corp and Wendy's.

In-N-Out, in response to Bloomberg's valuation, called it speculation. The company is private, its financials confidential.

In-N-Out, according to a 2003 Harvard Business School case study cited by Bloomberg, has never franchised, which helps it to maintain strict quality control. Consultants Bain & Co in 2005 estimated the chain enjoys a 20 percent profit margin, thanks in part to the company's focus on simplicity: its menu is strictly limited.

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According to the company's website, In-N-Out expanded into Texas in 2011, after building a new warehouse and patty-making factory in Dallas.

Torres, says Bloomberg, guards her privacy and grants few interviews. In September she bought a 7-bedroom, 16-bathroom mansion near the San Gabriel Mountains, according to Realtor.com. Her most visible presence so far, says Bloomberg, has been on the racing circuit. She competes in National Hot Rod Association races, sometimes driving a 1970 Plymouth Barracuda, sometimes a 1984 Chevrolet Camaro, according to association records.