The best shapes for genovese
Onions cooked down with beef over several hours until both collapse into a soft bronze cream. There is no tomato in it at all, which surprises most people meeting a Neapolitan sauce for the first time. The sweetness is entirely from the onion.
Naples' onion and beef sauce, cooked to a bronze cream, no tomato. Despite the name it is Neapolitan, and it belongs on ziti and candele broken by hand.
Canonical: ziti, candele, paccheri.

The wide round bore is the whole point.

A cooked pacchero rarely stays a cylinder.

Ziti is a smooth, even-walled tube, so it slips past thin sauces and asks for ones with real body.
What we would not put it on
Fine pastina and thin strands. The sauce has real body and needs a shape with enough structure to stand up in it.
Want it the other way around? Start from a shape in the Pairing Finder.
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From the Almanac
Updates from Pasta Almanac, when there is something worth sharing.