Black truffle of the Moianès Food and drink · Castellterçol, Moianès, Barcelona The holm oak and Portuguese oak woods of the comarca give black winter truffle, gathered with a dog between December and March. From an occasional supplement it has become a main product, with a market of its own and a presence on the menus of the area. Photo: Government of Catalonia (Attribution) What to see and do in Castellterçol