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1
Pour the olive oil into a wide, heavy pan set over the lowest possible heat. Add the very finely sliced white onion. Cook, uncovered, for 30–40 minutes, stirring occasionally, until the onion is completely transparent, soft, and without distinct form. Midway through, add the white wine and allow it to absorb. The onion must be entirely sweet and dissolved — any residual pungency means it is not ready.
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2
Add the desalted anchovy fillets to the dissolved onion. Stir continuously over the lowest heat until the anchovies are completely incorporated into the oil and onion — no visible pieces remain. The mixture should smell deeply savoury and unified, not sharp or fishy.
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3
Add the soaked, squeezed raisins to the sauce. Continue on the lowest heat for a further 5 minutes. The raisins must be plump and softened but hold their shape — they must not disintegrate into the sauce.
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4
Bring a large pot of salted water to a rolling boil. Cook the bigoli until al dente — the coarse, porous surface will carry the sauce; taste a strand to confirm it is yielding but with resistance at the centre.
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5
Drain the bigoli, reserving a small amount of pasta water. Transfer the bigoli directly to the pan of sauce. Toss over low heat, adding a splash of pasta water only if the mixture appears dry. The sauce should coat every strand in a thin, unified film — onion, anchovy, and raisin indistinguishable as separate elements.