In a medium bowl, combine 4 ounces finely chopped good-quality semisweet chocolate, 1 1/2 tablespoons unsalted butter cut into small pieces and a pinch salt. In a small saucepan, bring 3/4 cup water and 3/4 ounce good-quality jasmine green tea leaves (about 1/3 cup) to a boil; strain into a bowl, pressing to extract as much liquid as possible. Return the brewed tea to the saucepan, add 6 tablespoons heavy cream and bring just to a boil; pour over the chocolate mixture and whisk until smooth. Let cool for 30 minutes, then press a sheet of plastic wrap directly onto the surface of the chocolate and refrigerate for at least 1 hour. Shape teaspoonfuls of the chocolate into balls, then roll in unsweetened cocoa powder.