I was just in Herndon visiting my favorite local aquarium store, across the street from the former location of Mom's Pie Shop. To my surprise, the former Mom's is now the home of a branch of the Amphora Bakery (which has another location in Vienna). I popped in for a second and looked around; they have a very nice (and big) selection of cakes and pastries, and also serve coffees and pastries for consumption on the premises. They have seating on the main floor and a bit upstairs, from which you have a view of the extensive preparation area in the back. It seems that they are also installing a fireplace in one of the seating areas, and that they do event catering, too. I did not actually buy anything, so cannot report on quality, but it all looked quite good.
The location is on Sunset Park Drive, which is just left of the Fairfax County Parkway off of Sunset Drive (not quite sure about that street's name, but it's the street that the Target is on).