Brazil's national spirit, the rumlike cachaça, has risen in both quality and profile. Brazilian bartenders use it to replace other spirits in classic drinks like the Negroni and the mojito, but recently mixologists have been creating original cocktails with it. At Chez Oscar, a new, three-level restaurant with a rooftop bar in São Paulo, they serve it with tangerine juice and a puckering hit of lemongrass.