I tried parboiling broccoli for the first time today after having been introduced to the technique by Jeremy. Jeremy is studying to become a chef and probably picked up this technique at school. The broccoli comes out done perfectly (to my taste anyway) and with a much better color than by other methods. I'd even say it's better than steaming.
Basically the technique is to bring water to a rolling boil and then drop in the vegetables for just long enough (maybe a minute?). The idea is to cook it just barely enough and quickly. It's very similar to blanching except that you don't drop the food in cold water afterword. This is a great way to cook broccoli, carrots, or other dense or thick vegetables. It's also a good way to avoid adding too much water to a stir-fry.
We had a discussion with Dad a while back about the etymology of the word. Jeremy had assumed that "par" was the same as the word "par" as used in golf, for instance. Dad objected that if that were the case it would mean thoroughly boiled. As luck would have it they were both right! By some odd twist of fate parboil (which means to boil partly) used to mean to boil thoroughly. Perhaps boiling any longer than absolutely neccessary was considered too much, more than thorough.