Cheese pupusas - stuffed, griddled masa cakes - and their accompanying slaw, curtido, are quintessential Salvadoran street foods This recipe is adapted from Janet Lainez, who has been making them for homesick Latinos every summer at the Red Hook Ball Fields for nearly 25 years She likes to use mozzarella rather than Salvadoran cheese - preferably Polly-O, established in Brooklyn, 1899.