Soil, dirt, mud ... Call it what you like, the not-so-secret special ingredient at some of Japan's high-end restaurants has a distinctly earthy quality. And over the last couple of months, it's been getting substantial media attention, both at home and abroad.

For that, we can thank veteran chef Toshio Tanabe. He is so keen on serving soil as part of his haute cuisine that he's begun putting it in everything. His new tsuchi ryōri ("earth cuisine") menu includes as many as six courses. From the appetizer, perhaps a mud and potato potage with black truffle, right through to his dirt ice cream for dessert, all incorporate earth — real earth from the ground.

Is it a joke or some kind of macho challenge? After all, the name of his restaurant, Ne Quittez Pas, is French for "Don't Leave." Not at all: The soil is a mulch of coffee grounds and palm-fiber peat painstakingly prepared to render it safe and sanitary. Although the muddy color remains, there are no off-flavors or aromas left at the end to spoil your appetite.