Georgetown Cupcake owners Sophie LaMontagne (left) and Katherine Kallinis threw a party — a champagne and cupcake reception, actually — to celebrate the opening of their new shop on Newbury Street. The sisters, stars of the TLC show “DC Cupcakes,” opened their first shop in D.C. in 2008. Why Boston? Because LaMontagne knows the area, having worked for a venture firm before she started selling cupcakes.