“When two are served, you may begin to eat.”

Here’s a longer explanation from Nathan Brackett:

The elegance of Futterman’s Rule does lend it a hint of spirituality. One eats one’s food while it is hot, observing dinner as a natural continuum (instead of the top-down, “no-one-eats-until-the-chef-is-ready” hierarchical model that dominates most households). At the same time, no one eats alone (it is only once two people are served, and a social base is established for those with food, that one may begin to eat). If form follows function, the Rule is built to travel. So give it a try. And if you like it, tell a friend.