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The line extends almost out the door of this newly opened restaurant in the East Village. Inside, the tables are full and dozens of people wait expectantly for their food under the peculiar orange-and-yellow lighting.

But a celebrity chef does not own this buzzing sliver of space. The menu is not dotted with trendy, grass-fed lamb, overpriced fish or organic staples like heirloom tomatoes and beets. You can't even get wine -- not yet anyway.

No, this is S'MAC, or Sarita's Macaroni & Cheese, the newest niche eatery in New York City.

"It's been awesome," said Sarita Ekya, who started S'MAC with her husband, Caesar. "We didn't realize how popular we'd be."

Across the country and especially in New York City, tightly focused menus that serve a variation on a single theme are prospering and spreading.

From cereal to peanut butter, rice pudding to gourmet dumplings, haute desserts to grilled cheese, restaurateurs are trying to cash in on comfort food.

"We thought it would do well because we're selling a product everybody loves," said Kenneth Rader, who opened The Cereal Bowl in Miami in February with his brother, Joshua. "There's no one who hasn't grown up on cereal."

While niche restaurants continue to pick up popularity in the world of mainstream dining, Rader and the others certainly didn't invent this savory concept.

In the Chinatowns of New York and San Francisco, dumpling joints have long been food de rigueur. Taquerias and pupuserias, along with falafel stands, can be found on many street corners in multi-ethnic neighborhoods.

Perhaps the greatest, and most lucrative, of these one-food wonders is the revered pizza parlor.

But these culinary home runs and their successors have plenty in common. They resonate with people. That's the trick, says Lee Zalben, who started Peanut Butter & Co. in New York City in 1998.

"It's important to find something that marries mass appeal with novelty," Zalben said. "It needs to grab the customer's attention. You have to be offering something they want to eat a couple of times a week. We found something that really appeals to people. Peanut butter is America's favorite sandwich."

It was Zalben's place that inspired S'MAC. Sarita and Caesar pay homage to Zalben on their Web site, admitting their inspiration came after eating at Zalben's little shop last year.

"We left ... and thought, 'mac and cheese, there's a need for this'," Sarita said.

Tapping their savings and small business loans, they raised $200,000 and opened the 30-seat S'MAC in June. Then the hungry and sentimental hordes descended.

Sarita and Caesar were quickly overwhelmed despite not spending a dime on advertising (Internet buzz and two prominent New York publications helped spread the word).

The pair thought they would have to prepare only a dozen or so dishes an hour in the cramped kitchen, open only for dinner and employ three people.

Those conservative estimates soon popped, along with the notion that Sarita and Caesar wouldn't be sleeping much, as they shepherded this restaurant out of its infancy.

Now, S'MAC has hired 14 people and serves an average of 300 meals a day for both lunch and dinner. At peak hours, S'MAC is jammed with folks tempted to try the recipes.

S'MAC turns out a variety of cheesy concoctions in iron skillets that come in three different sizes. S'MAC uses wheat and regular, Barilla twisted-elbow macaroni and cheeses such as manchego, Brie, Parmesan, Gorgonzola and Gruyere.

The food is ready in a matter of minutes. It has to be. Like other restaurants of the same ilk, S'MAC is a volume business. Caesar calls it "quick-serve" food.

Zalben says he's flattered that he inspired S'MAC. And the godfather of peanut butter has some encouraging words for Sarita and Caesar.

S'MAC could have legs.

"It looked like a great concept," Zalben said.

Sarita and Caesar hope so. They have big hopes for their little idea. There could be a franchise and frozen-food line in the works one day.

"It's gonna be the next pizza," Caesar said boldly. "There are other concepts that you can stretch so far but this is endless."