The truffle is the fragrant underground fruiting body of certain Tuber fungi — above all the black Périgord truffle (Tuber melanosporum) and the white Alba truffle (Tuber magnatum) — knobbly, soil-coloured lumps that grow buried among the roots of oak and hazel and must be sniffed out by trained dogs or pigs. Hidden in the dark, they evolved an extraordinary aroma to lure animals into digging them up and spreading their spores, and that aroma is their whole point: deep, musky and earthy in the black, intensely garlicky-sulfurous and almost gassy in the white. Pungent enough that a single nut perfumes a room, and heat-fragile enough that the classic treatment is to shave it raw and paper-thin over a warm plate of eggs, pasta or risotto, the truffle is the aromatic apex of the fungal kingdom — and, by weight, among the most expensive foods on Earth.