There is no consensus. According to the most celebrated of all Swiss chefs, Fredy Giradet, rösti are made with boiled potato while pommes paillasson are made with raw potato. But in Zurich rösti are made with raw potato . . . and the finest I’ve eaten was at Kronenhalle in that city, after an exhibition of my favourite painter. The finest pommes paillasson were from Olivier Traiteur at the Marché des Grands Hommes in Bordeaux; almost certainly cooked from raw.