I went there about 5 years ago with a friend to pick up a croquembouche for her mother's anniversary party. I ended up holding the 3' high pastry in my lap all the way back to La Plata because the chef (who followed us all the way out to the car to oversee the transportation arrangements) insisted that it could not be put in the back seat under any circumstances.

According to the Yahoo Yellow Pages, the bakery is still there:
Desserts By Gerard
6341 Livingston Rd, Oxon Hill, MD 20745
(301) 839-2185

By far Old Town's best bakery, the breads are exceptional too and worth the short trek over the bridge. Ditto on Adelman's post on Firehook Bakery

At the risk of dating myself, I hadn't been to Desserts by Gerard in SEVENTEEN YEARS. This is a valuable source for Breadline baguettes, but since I wanted to try their own wares, I got an outsized Brioche Bun to have with my tubs of Tuna Salad and Chicken Salad, a Tarte aux Fruits, and a slice of Carrot Cake.

Everything was good except the fruit tart, which had a croissant-like shell and a LOT of corn starch in the pastry creme. The fruits themselves were very good, and the carrot cake was one of the best versions I've found in this area, with an elegant Chantilly-like frosting that had just the right absence of sweetness for the moist, well-made cake. The chicken-salad was eggy, and too many corners were cut by the extensive use of apples as filler; I barely remember finding any chicken. But the puree-like tuna salad, with its touch of oregano, was an elevated version, and the brioche worked well as a sandwich pocket despite it being slightly dry.

I can see flaws in Gerard's that I probably wouldn't have noticed seventeen years ago, but this still remains an excellent patisserie. If you're going to visit National Harbor, consider going to Desserts by Gerard first (exit 3B on the outer loop), grabbing a pastry picnic, and then heading over to grab a bench by the water.

Cheers,
Rocks.