Melt the chocolate and cream in a double boiler over hot but not simmering water. Place melted chocolate in a small bowl. Stir in the balsamic vinegar. Cool the chocolate in the refrigerator for 1 hour. Remove from the refrigerator and let sit at room temperature for 2 hours, until firm but moldable.
Use a teaspoon to scoop out chocolate. Use your fingertips to shape into balls about the size of a cherry. Set the chocolate balls on a parchment-lined tray.
Place the cocoa powder in a small shallow dish. Place 6 truffles at a time in the cocoa powder and roll the truffles around to coat, and return the coated truffles to the baking sheet. Continue with the remaining truffles. Place the truffles in a serving dish or airtight package.