"Georgetown Cupcake" sisters Sophie LaMontagne and Katherine Kallinis with Candace Bushnell at the book party for "Summer and the City" Tuesday in Foggy Bottom. (Paul Morigi)

Every time we think the cupcake fad must be dying out, the lines at Georgetown Cupcake prove us wrong. The buttercream junkies keep coming (Sasha Obama celebrated her 10th birthday there earlier this month), and the little pink-and-brown shop has become a tourist landmark.

Now the D.C.-based franchise is headed to New York. Owners/sisters Sophie LaMontagne (the blonde one) and Katherine Kallinis (the brunette) have announced the expansion of their business to Manhattan; they’ll be filming the third season of TLC’s “DC Cupcakes” around the Soho launch later this year.

“D.C. will still be our home base, but we had so many people in New York asking us to open,” said Sophie at a book party Tuesday for “Sex and the City” author Candace Bushnell.

Customers form a line up 33rd Street from the door of Georgetown Cupcakes. (Bill O'Leary/The Washington Post)

In just three years, the sisters and their critic-proof cupcakes have managed to dominate the local market with locations in Georgetown and Bethesda, the reality show, and a cookbook coming out this fall. Katherine got engaged to Washington lawyer Ben Berman on the final episode of season two this spring; of course, their September wedding in Santa Barbara will be an hour-long special of the show.

“There’s going to be a cupcake tower like you wouldn’t believe,” promised Sophie. “I’ll do it myself. I’m not going to make her do it.”

“Yeah,” scoffed Katherine. “She says that, but I’ll be in my wedding dress frosting something.”