If you’ve ever built a gingerbread house, you know that walls crack, icing flakes, and roofs sag — if they don’t collapse altogether. And once you’ve got your gingerbread house up, you’ve got to maintain and protect it against sticky humidity and sticky fingers. In the spirit of the holidays, we recently talked with a handful of chefs who spend at least a couple of months each year constructing gingerbread houses — even cities — for private and corporate clients. Here are t