Preparation

Put balsamic and zest into a small pot and bring to a boil. Reduce heat and simmer 5 minutes.
Set aside to cool.
Melt chocolate and cream in a double boiler (or a heat-proof glass bowl over a pot filled with water), making sure the water is hot, not boiling.
Place melted chocolate in a small bowl and add the cooled balsamic. Mix well.
Cool in the refrigerator about 1 hour. Let sit at room temperature for 1 hour, until firm but moldable.
Roll mixture into one inch balls and place on a parchment lined tray. Pour cocoa powder into a shallow dish and roll balls to cover.
Serve immediately or store in an airtight container up to one week.