Jansson's Temptation

Instructions

1. Heat the oven to 200C (fan 180C). Peel 250 g of floury potatoes and cut them into even matchsticks about 5 mm thick, a mandoline with a julienne blade or a steady knife both work. Do not rinse or soak them: the surface starch is what binds the cream into a sauce. Keep them wrapped in a dry tea towel while you work.
2. Slice 60 g of onion paper-thin. Melt 5 g of the butter in a small frying pan over low heat and sweat the onion for 6-8 minutes, stirring, until soft and translucent but with no colour at all, browning would make the dish taste bitter against the anchovy.
3. Drain 35 g of Swedish anchovy fillets, reserving the brine, and chop them coarsely. Lightly butter a small gratin or pie dish of about 15 cm.