The workaholic sisters from the TLC show D.C. Cupcakes are rolling up their sleeves ... but not for buttercream frosting. The girls are officially getting to work on the construction of their new Mercer Street location, their first in the city after years of nonstop Washingtonian worship. They tell Grub Street that the entire build-out will be filmed for a one-hour episode, kicking off the new season of their show. GT Cupcakes is set to open this winter, and from the looks of it, they better install their coffeemaker first. There's a lot to be done. "We cannot wait to open!!!" Katherine, tells us.