LOS ANGELES — When Hee-sook Lee opened a restaurant at the edge of Los Angeles' Koreatown more than a decade ago, there seemed to be nothing remarkable about the tofu stew she served.

But with a "secret recipe" for the common Korean dish and an entrepreneurial side that family and friends had never seen in her, Lee within a few short years was exporting her brand of tofu stew to South Korea, building a small empire that has spawned numerous imitators.

Today, tourists from South Korea arrive by the busload at BCD Tofu House and snap photos. Visiting dignitaries, sports stars and actors frequently dine at the restaurant. Even though the restaurant is open around the clock, there is almost always a wait.

Since the Vermont Avenue restaurant opened in 1996, Lee has expanded it into a trans-Pacific chain with more than a dozen branches in Los Angeles, Seattle, Tokyo and Seoul. And she is far from being done.

"It's not important whether there are 10 or 100 branches," Lee said, speaking in Korean. "I consider myself a diplomat of sorts, making Korean food known to the world."

The success of Lee's restaurants has catapulted the immaculately dressed 48-year-old chief executive into minor celebrity status in South Korea. People recognize her from numerous media reports and approach her on the streets of Seoul.

The South Korean government invited her to speak at a convention for overseas Korean business owners. In 2006, the tale of her success was re-enacted in a 12-part radio mini-series broadcast in South Korea.

Fellow immigrants look to Lee for a clue as to how she built up a business that brings in $19 million annually and employs more than 300 people. Many wonder how a common dish brimming with very Korean flavors — spicy, salty and served scalding hot — succeeded in Los Angeles.

To those asking for the secret to her success, Lee smiles and says there really isn't much to it.

"To succeed in anything, you just have to be fanatically devoted to it," Lee told a hall full of dark-suited business people at the government-sponsored convention in 2006. "No matter what other people tell you, you shouldn't look back."

When she arrived in Los Angeles with two of her three sons in 1989, Lee barely spoke English. She left behind her husband, Tae Lee, and 18-month-old son so that she and the other sons, 5 and 7 at the time, could get an education.

Initially, the plan was to return to South Korea after a few years. She studied design at Santa Monica College and then moved on to the Gemology Institute of America. But when Lee finished her studies, the children had grown attached to life in the U.S. and didn't want to move back.

Lee toyed with the idea of permanently settling here and wondered what she could do to earn a living. Having married young, her experiences were limited — a brief stint as an accountant and helping operate a restaurant owned by her husband. But Lee was convinced that she could thrive as a businesswoman, she said.

She decided to take a gamble and open a restaurant. And entering the restaurant business was no small gamble. A quarter of all new restaurants close by the first year, and by the third year nearly half shut down, according to the California Restaurant Association.

To differentiate her eatery from the seemingly endless restaurants lining the streets of Koreatown, Lee decided she would serve just one simple tofu dish, "soon-dubu" — a common, cheap lunch dish with chunks of white tofu submerged in a bubbling bright red soup saturated with spices.

Lee took to the kitchen, spending long nights experimenting with spices and condiments. From the commonplace stew, she conjured up 12 varieties with different meat and flavors. She brainstormed ways to customize the dish like a cup of coffee, offering four degrees of spiciness, with or without monosodium glutamate. Her final recipe is a secret that she won't share with anyone, not even her husband, she said.

After about a year of preparation and some advertising, Lee opened her first BCD Tofu House on Vermont Avenue in April 1996. The name is short for Buk Chang Dong, a neighborhood in Seoul where her in-laws once ran a small restaurant.

Lee spent much of her time tending to the restaurant's operation. Each day at 2 a.m. she went to the downtown wholesale market to handpick produce. Three months after her restaurant opened, Lee and her family, who were reunited, moved to Las Vegas, where her husband owned property and the residency application process was shorter. She commuted to Los Angeles by plane each day to oversee her restaurant's operations.

"I wanted to be home by the time the children got home from school and cook them dinner, so I would take the 6:30, 7:30 flight back. ... The children would get tired of waiting and fall asleep, and that was painful for me to see," Lee recalled.

Ten months after the first restaurant opened, Lee opened a second BCD Tofu House in Koreatown. Ten months after that, she opened a third in Garden Grove.

"I could have just operated one restaurant to perfection, but anyone could do that," Lee said.

Just two years into the business, Lee began to export her soon-dubu to South Korea. Now she operates 13 tofu houses on either side of the Pacific and plans to open two more in Irvine and Fullerton in the coming months. Lee, who became a naturalized citizen in 2000, says she wants to eventually open branches on the East Coast and in China and to franchise the chain in the U.S.

Even at this rate, Lee hasn't been able to open branches fast enough to keep up with the demand, and numerous imitators are taking advantage of the opportunity. One chain calls itself "BSD" and has nearly 50 franchises throughout South Korea, Japan, Taiwan and China.

Last July, Lee faced a restaurateur's worst fear — a food poisoning report to the Los Angeles County Department of Health Services. When the restaurant on Wilshire Boulevard was closed for nine days as a result of an inspection, the Korean media in Los Angeles reported on the story daily, treating it as front-page news because of the restaurant's popularity. Rumors that the restaurant was unsanitary circulated in the Korean community, and the flow of customers ebbed for a while, Lee said.

The experience was especially painful for Lee because she tries to keep a tight rein on the restaurants' operations. Each day, she makes about 40 gallons of her secret seasoning which is shipped to all her U.S. restaurants. When she visits one of her restaurants, she listens for the clatter dishes make when carelessly placed on the table and looks for the one customer in the corner who has been waiting too long to be served. For first-time diners who look a little lost, she will even show them how her food is to be eaten.