Umbria, particularly the Nera Valley and the Valnerina around Norcia. Black truffle harvest season is December-March; this pasta is specifically a winter dish tied to the truffle season.
Strangozzi (also called stringozzi or umbricelli — terminology varies by village) are a thick, hand-rolled pasta similar to pici: a rough, irregular-surfaced spaghetti made from water and flour only (no eggs), rolled by hand on a wooden board. They are the ancestral pasta of the Umbrian shepherds and pilgrims. Dressed with the black truffle of Norcia, which is grated and dissolved into the pasta's cooking oil with garlic to create an intensely aromatic, earthy sauce — a preparation that showcases the truffle without any enriching dairy or cream.
Properly made, this is one of the most profound pasta dishes in Italy: the warm truffle oil is deeply earthy, heady, and complex; the rough strangozzi grips and carries the oil in every groove; the garlic is barely perceptible as a background warmth. The flavour expands on the palate for a full minute after the bite — the mark of fresh, quality black truffle.
The hand-rolling of strangozzi creates the characteristic slightly irregular surface — rougher than machine-made pasta, which grips the oil-truffle sauce in every groove. The black Norcia truffle (Tuber melanosporum) is a cooked truffle — unlike white truffle, which is served raw, black truffle must be warmed to release its aromatic compounds. The classic dressing: a generous amount of good Umbrian olive oil, garlic gently warmed (not fried), then the grated black truffle stirred into the oil off heat. The cooked, drained pasta is tossed in this sauce — the pasta water loosens and emulsifies the oil. No Parmigiano, no butter — black truffle with oil and pasta only.
The most common error in truffle pasta is using insufficient truffle. A great serving (15-20g of fresh black truffle per portion) produces a completely different experience from a 'hint' of truffle. The oil should be warm, not hot, when the truffle goes in — if the oil sizzles, it's too hot. The aromatic compounds in black truffle are volatile; keep the pan off high heat.
Adding cream or butter — they mask the truffle aroma. Frying the garlic until golden — it overpowers the truffle. Grating truffle over the finished dish without warming it — black truffle needs gentle heat to release its compounds. Using jarred truffle or truffle paste — the thermal processing has eliminated the volatile aromatics that make this dish worthwhile.
Faith Willinger, Eating in Italy; Slow Food Editore, Umbria in Cucina