Often lauded as the optimal bun for smashburgers, the squishy, yellow potato roll has been a holy grail for burger geeks around the country. The reigning champ among those buns has to be the one from Martin’s Famous Pastry Shoppe, a family-owned company based in Chambersburg, Penn. It catapulted to fame with the rise of Shake Shack, which uses its bread exclusively at its locations around the world. Locally, use of the Martin’s potato bun, at operations like Wesburger, Kowbird and Smish Smash, has signified chefs’ seriousness about their sandwiches.