Today I watched an episode of "Julia & Jacques", in which they were making a haricots vert dish.
I wasn't listening closely, but I noticed Pepin heating what looked like a long, massive, ancient soldering iron over a gas hob adjacent to the boiler. As soon as the haricots were dumped into the boiling water, he took the implement (it had a wooden handle) and plunged IT into the center of the boiler. The water IMMEDIATELY came back to a roiling boil. Brilliant!
Obviously, the intent is to give the water a heat boost to keep it at a boil, and therefore to keep the vegetables from going soggy.
What are these really called, and has anyone used one? If so, do they work as well as it appeared, and where did you find yours?