Peel the onions, cut in half lengthwise and slice very thinly. Heat the oil in a wide-based pan, add the onions and sweat over a low heat without allowing them to colour, adding a little hot water if they become too dry. Meanwhile, wash and de-salt the anchovies (or sardines), clean them well and cut into small pieces. Cook the onions until transparent. Add the anchovies and let them melt slowly and completely, adding a little of the pasta cooking water if necessary. Add pepper to taste. Cook the Nonna Rina bigoli to al dente, then transfer to the pan with the hot sauce, stirring so the bigoli absorb the flavours.