The walnut pieces are boiled to remove excess bitterness; this is a great technique and it really does work!
It may take more than one try to unmold the Panna Cotta. Don't dispare, just keep dipping and jiggling.
Ingredient Notes
Use the best quality aged balsamic vinegar you can find (or afford).
This is a chef's recipe, so naturally he calls for an ingredient that you can't just pick up in any grocery store. You can find it in plenty of places online.
Source/Adapted From
Chef Joseph Wrede, New Mexico