A small family restaurant in downtown Smithfield, El Castillo runs Salvadoran and Mexican cooking side by side on one menu. Its pupusas and tamales are made by hand every day, sharing the menu with tacos, burritos, and an early breakfast service. Orders go over the counter, fast and often in Spanish, in a clean dining room with no pretense. North of Logan, it’s the easiest place to try Central American flavors.