So completely does the citrus-flavored fortune cookie dominate the dinner tables of Chinese restaurants in New York, it is small wonder that its chocolate-flavored cousin survives at all. But there is such a thing as a chocolate fortune cookie, and for the last 10 years, it has popped up in pockets of neighborhoods, like Park Slope, Brooklyn, where it is usually met with delight or confusion.

Some New Yorkers may even doubt its existence, but perhaps that is only because this cookie's story is as hardscrabble as it is little known. "I've lived here all my life, and never once have I seen a chocolate fortune cookie," Javier Torres, a mailroom supervisor who eats Chinese food twice a week, said the other day as he stood at the counter of Young Chow, a Chinese takeout place near Union Square.

Once, citrus and chocolate competed in the city as equals against that original of fortune-cookie flavors, vanilla. To learn about this quiet battle and to discover why chocolate has the lowest profile, one would do well to visit the country's biggest maker of fortune cookies, Wonton Food.

At Wonton's Long Island City factory, more than two million fortune cookies are turned out a day, but only about 5 percent are flavored with cocoa powder, said Alex Luk, a spokesman. The company came up with the idea a decade ago when it learned that smaller fortune-cookie factories in San Francisco, the cookie's historical home, had started experimenting with flavors. Wonton had used only vanilla since its founding in 1983, Mr. Luk said, as had the Japanese couple whose company had produced most of the city's fortune cookies before Wonton arrived on the scene.

"We really pioneered the citrus and chocolate flavors, but it was the citrus that took off," Mr. Luk said.

Chocolate was not the only disappointment. Strawberry and peanut butter cookies were shelved, and the latest attempt, a triflavored version, has barely gained a following. So, how has chocolate endured?

Through wholesale suppliers, mostly. Wonton relies on a network of more than 30 companies to distribute its cookies to local restaurants. In the flush of competition, these companies often try to carry as many kinds of products as possible.

One place that offers the chocolate option is Uncle Liao Restaurant on Fifth Avenue in Park Slope. When it opened 10 years ago, it offered vanilla-flavored cookies, said Cathy Liao, who helps run the family business. But five years ago, their local supplier mentioned how tasty the chocolate ones were. Ms. Liao does not like fortune cookies, period, but her young daughter tried them all and liked chocolate best. Uncle Liao has ordered 2,500 chocolate fortune cookies a week ever since.

"We like the idea of being different," she said, though she acknowledged that Red Hot Szechwan, two blocks away, also gives away chocolate cookies.

Fans include Angelo Salas, 8, who eats at Uncle Liao at least once a week with his mother and a family friend. Angelo usually eats all their cookies, and the chocolate kind is rare enough to be considered a treat. "I like anything that's chocolate," he said.