In the weeks leading up to the grand opening of their cupcake shop in Georgetown, Katherine Kallinis Berman and Sophie Kallinis LaMontagne caught a case of cold feet.

Although the two sisters had long shared the dream of starting a bakery together, they knew the odds of success were stacked against them.

“All we knew was that we loved to bake and wanted to work together, but the conversation about whether to go for it was scary,” says Berman.

“Half of new restaurants fail within the first year, and we were afraid we would, too,” adds LaMontagne. “We had every reason not to open a bakery.” Their parents begged them not to leave their lucrative jobs —LaMontagne, in venture capital; Berman, in fashion—for the baking business. Bankers turned them away for small business loans, so they had to max out their personal credit cards. Even the contractors who helped renovate their first location had their doubts.

“They would just shake their heads and say: “You’re going to start a business selling cupcakes?” says Berman. “Then they would kind of laugh.”

Five years and four more stores later, Berman and LaMontagne are the ones laughing. The smart, business-savvy sisters are enjoying the meteoric rise of Georgetown Cupcake and seem thrilled but bemused by how they transformed a family-run neighborhood bakery into a bona fide brand with recognition well beyond the District’s borders.

“We opened that first day and wondered if anyone would come, or even care,” says Berman. “But shortly after we opened, a line formed. The next day, there was another line. It’s never stopped.” With stores now open in Bethesda, Boston, New York, and Los Angeles, they lead a staff of 400 who bake on average a staggering 20,000 cupcakes a day for legions of loyal customers. They’ve also authored two hit cookbooks—the most recent, Sweet Celebrations, was released in October by HarperOne, an imprint of HarperCollins—and star in their own reality TV show on TLC: DC Cupcakes offers an insider look at their day-to-day work and sisterly dynamic.

“They’ve made the experience of buying cupcakes very special and fun, from the pink-box packaging to the innovative flavors that rotate seasonally,” says Nancy Miyahira, marketing director of the Georgetown Business Improvement District. “They’ve put a lot of thought and creative details into the store, the experience, and the product.” Even in extreme weather, fans of Georgetown Cupcake regularly stand in line outside each of the store locations. In Washington the line is legendary, snaking outside the front doors and well up on 33rd Street.

Why endure the wait? First for the cupcakes themselves, which are divine. Baked with only the best ingredients, they’ve won over legions of foodies, including the legendary critic Frank Bruni of The New York Times, who praised them as some of the best he’d ever tasted. They are also a study in perfection—iced and decorated with an artisan’s touch. The combination of taste and style makes them hard for even the most restrained dieter to resist.

But it’s not just the cupcakes, the sisters explain, that have earned them fame and fortune in the business of baking. “People stand in line by choice [cupcakes can be ordered online]... for the whole experience,” says LaMontagne. “It’s a magical store where music is playing, people are happy, and they can see the cupcakes being made and iced by hand.”

Inspired by years spent baking with their Greek grandmother, both women work around the clock to cater to their customers. Their brand of personal service has also attracted a celebrity clientele; Georgetown Cupcake has delivered signature sweets to everyone from Kim Kardashian to Sasha Obama, who celebrated her birthday at the store.

Miyahira and other local business leaders say they are grateful for the attention. “We’re very fortunate that they chose to use the neighborhood’s name.... It spreads awareness for Georgetown as a special destination.”

Business is booming for a little shop that started with nothing more than two sisters and a dream, but it’s clear that the best might be yet to come. They’ve already got a third cookbook in the works, and are on the lookout for additional store locations.

“We love what we do,” says Berman, who is pregnant with her first child. “And maybe one day we can pass it down to our kids and keep it in the family.”

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