You might expect to find sustainably sourced, wild-caught fish on the menu of a high-end seafood restaurant, but probably not during a lunchtime grazing run at a farmers market. Chef Henry Brandon Williams is angling to change that expectation, at the FreshFarm Market by the White House. Every week since the beginning of May, his Fish Scale stand has been offering two sandwiches made with eco-conscious fish from J.J. McDonnell in Jessup and ProFish in the District.

The idea came to the 31-year-old Laurel resident when he was casting about for something to serve his pescatarian mother at a barbecue in the summer of 2008. She was eating mostly trout and croaker, so Williams set out to broaden her horizons by making her a red snapper burger.

“She almost didn’t get one, because all the meat eaters were grabbing them up,” he says.

Heartened by the response and inspired by his own organic diet, Williams decided to turn the idea into a business. To hone his kitchen skills, in 2009 he enrolled at L’Academie de Cuisine, for study that included an externship at BlackSalt in the Palisades.

His hard work pays off in a big way when you nosh at Fish Scale. A round of Carolina-caught mahi-mahi is lightly dressed with a few ribbons of pickled kimchi sporting a fiery red pepper finish ($10). It’s presented on a golden-topped, soft olive oil bun from Panorama Bakery. Williams says he considers the bread a key element. “It can make or break a burger,” he says.

Biting into the patty, I find a moist core that hides the barest hint of sweetness. The ample quarter-pounder is seasoned with just a sprinkling of sea salt that Williams adds while grilling it over the hardwood charcoal. “When you do less, you actually do more for the meat,” he says.

The second sandwich, made with grouper from the Gulf of Mexico, has pleasant sparks of brine and lime ($10). Those natural flavors are complemented by a thin layer of piquant, house-made harissa bolstered by flashes of preserved lemon, serrano pepper and cumin. There’s also a slather of a simple cucumber-tomato relish, which tempers the heat. Because each burger is cooked to order, you will have to wait a few minutes while it’s prepared. It’s also advisable to arrive early: Fish Scale has sold out before the close of market each week thus far.

Williams will be crafting burgers from a rotating cast of fish as the seasons change. Expect to see salmon, rockfish, tuna and black sea bass.

The operation hinges on its stripped-down approach. Williams’s mother, Mary Williams, and his sister, Kristal Williams, take orders at the stand. The chef also has roped in his father and his cousins to help out. Though the sign indicates that fries are available, Williams is saving those for the bricks-and-mortar version of Fish Scale that he says he hopes to open in the District in the next year or two.

— Nevin Martell

Fish Scale (at the FreshFarm Market by the White House) 810 Vermont Ave. NW; Hours: Thursdays, 11 a.m. to 2:30 p.m., while the market is in session.