Tourists passing through the old Harborplace pavilions may have to do a double take when they see Food Network champion David Thomas and his chef wife Tonya behind the counter of the former Johnny Rockets.

The foodie couple’s latest pop-up, the Nostalgia Diner, is serving comforting classics — including a reinvention of the pit beef sandwich — in the last place you might expect to see them.

For many in Baltimore, the Thomases need no introduction. David was a winner on TV’s “Chopped,” while Tonya has been a James Beard Foundation fellow. The couple opened Ida B’s Table in downtown Baltimore years ago before launching their own catering company, H3irloom Food Group, through which they have offered headline-grabbing dinners and explored ways to transform the local food system.

Now they’ve transformed the pit beef sandwich. A Baltimore staple going back to at least the 1970s, the dish is typically slathered in sliced onions and tiger sauce. Strip club-adjacent Chaps is one of the most famous spots to find it, but you can also find it at fundraisers, weddings and outside hardware stores.

While many eateries serve turkey and pork along with the traditional beef, “no one has done pit lamb,” Tonya said. Lamb doesn’t always get a lot of attention in the U.S. but is everywhere in West Africa, a region that heavily inspires the Thomases' approach to food. The pit lamb sandwich in particular pays homage to lamb dibi, a popular Senegalese street food served with onions and mustard.

While the sandwich will be a regular feature at their Harborplace pop-up, other menu options will rotate weekly, with an emphasis on comfort food. During a recent visit, that included a curry chicken biscuit pot pie reminiscent of a breakfast cobbler that the couple served at Ida B’s, as well as slices of cake.

Open Fridays and Saturdays from 11 a.m. until 6 p.m., the Nostalgia Diner will offer extended hours during the CIAA Basketball Tournament starting in late February before expanding its operations to run Wednesday through Sunday.

Sometime this summer, the Thomases also plan to open another eatery at Harborplace that could include an outdoor grilling component.

Johnny Rockets closed years ago amid Harborplace’s long, slow decline. The mostly empty shopping mall is slated for demolition and a nearly $1 billion overhaul. But the 1980s-era development has quietly become a culinary hub in recent months as MCB Real Estate looks to showcase possibilities for its future. With their pop-up, the Thomases hope to paint a brighter picture of what’s to come.

“Everybody knows that it’s [Harborplace] going to be torn down in roughly two years, but there’s still businesses down here that are trying to thrive and survive,” David said.

The Thomases are just the latest to set up in Harborplace. Other businesses have included Angeli’s Pizzeria, which has a presence on the second floor of the Light Street pavilion, and Oleum Vegan Kitchen, located near the entrance of the same building. But operating in an all-but-abandoned location has come with some challenges. Vendors have reported issues with equipment and low foot traffic, and some eateries have shut their doors. Crust By Mack closed its restaurant there last year, citing high operating costs.

For their part, the Thomases are working to help bring the masses back to the water, one pit lamb sandwich at a time. “We want people to believe in the Harborplace again, like we do,” David said.

This post has been updated.