For the Bittersweet Chocolate Truffle Base:
1-1/4 Cups heavy whipping cream
9 oz high–quality bittersweet chocolate (70% cocoa), chopped, divided
For the Chocolate coating:
8 oz high–quality bittersweet chocolate (70% cocoa), chopped
Unsweetened cocoa powder (optional; for rolling)
For the Base:
Bring cream to simmer in heavy small saucepan. Remove from heat; cool until lukewarm, 10 minutes. Stir in aged balsamic vinegar.
Meanwhile, stir 7 oz chocolate in metal bowl over saucepan of simmering water until smooth. Remove from heat. Add the remaining 2 oz of chocolate; stir until smooth. Stir in cream-balsamic mixture.
Chill truffle base until firm enough to roll, about 3 hours.
Line rimmed baking sheet with waxed paper. Roll 2 tsp of chilled truffle base between fingertips to form a ball. Transfer to prepared sheet. Repeat with remaining truffle base. Chill until firm, about 1 hour.
For chocolate coating:
Line another rimmed baking sheet with waxed paper. Stir bittersweet chocolate chunks in metal bowl over saucepan of simmering water just until melted. Remove from heat. Cool slightly.
Scoop some of warm (not hot) melted chocolate into palm of hand. Place 1 chilled truffle in hand and roll in palm to coat. Transfer to prepared sheet. Repeat with remaining melted chocolate and truffles, rewarming chocolate if necessary. Roll in cocoa powder if desired.*
Chill coated truffles until firm, about 1 hour.
Truffles can be made up to 1 week ahead. Store in airtight container and keep chilled. Let stand at room temperature 1 hour before serving.
*For variations, consider rolling in a mix of equal parts unsweetened cocoa and cinnamon, or roll in confectioners’ sugar, or finely chopped nuts such as pistachios or hazelnuts.