The crostino al tartufo is the open-face Italian toast in its most restrained register. A small slice of bread is toasted firm and topped with a thin layer of truffle, usually as a crema, the truffle worked into a smooth paste with a neutral fat, sometimes with a few shavings of the fresh fungus laid over it. It is a single slice with a single topping, eaten in a bite or two, and the defining fact is not what is added but how little of it. Truffle is loud and short-lived on the palate, and the entire discipline of this crostino is to use the smallest quantity that still reads, on a base plain enough to let it.
The craft is restraint and the base. The bread is taken small and toasted dry so it stays rigid under the spread, the same one-surface logic that governs every crostino: there is no second slice to balance against, so the topping has to be measured rather than generous. The truffle crema is spread thin and even, because a thick layer does not taste more of truffle, it tastes of the oil it is suspended in. Where fresh truffle is shaved on top it goes on at the last moment, off the heat, since warming it past a certain point flattens its aroma into nothing. The toast is kept faintly warm, not hot, so it firms the base without driving off what little volatile aroma the truffle carries.
This is the quiet cousin of the genre, and its louder relatives keep their own pages. The coarse, warm chicken-liver version, the fegatini spread thick rather than measured thin, is the Crostino Toscano; the seasonal vegetable and cheese crostini follow the same single-slice rule with their own toppings. Each is one slice under one thing, judged by restraint, and each deserves its own article rather than being crowded in here.