-
1
Pour the olive oil into a wide, heavy pan set over the lowest possible heat. Add the sliced onions and spread them flat. Cook, stirring occasionally, for 30–40 minutes. The dish lives or dies here: the onions must collapse entirely into a soft, sweet, uniform mass with no residual sharpness or texture — taste them; any bite or pungency means more time is required.
-
2
Add the rinsed, de-spined anchovies to the collapsed onion base. Stir continuously over gentle heat. The anchovies will begin to dissolve; continue stirring until no visible piece of anchovy remains and the oil and onions have absorbed them completely into a single, uniform sauce. Add no salt — the anchovies provide it.
-
3
Bring a large pot of unsalted water to a full boil. Cook the bigoli until al dente according to the pasta's weight and thickness. The surface of bronze-die bigoli will appear rough and dull rather than smooth — this is correct, and it is what holds the sauce.
-
4
Drain the bigoli, reserving a ladleful of pasta water. Transfer the pasta directly to the pan of sauce. Toss over low heat, adding a little pasta water if needed to help the sauce coat every strand. The finished dish should be glossy, with the sauce clinging evenly to the rough surface of the bigoli — no pooling liquid, no dry patches.