Imelletty Perunalaatikko

Method

1. Put 300 g of peeled, evenly chunked floury potatoes in a small saucepan, cover with cold water, salt it lightly and bring to the boil. Simmer 20-25 minutes until a knife slides through with no resistance.
2. Drain well and return the pan to low heat for a minute to steam off the surface water. Mash thoroughly with a masher or press through a ricer — the mash must be completely lump-free, as lumps stay hard through the long bake. Leave uncovered until it has cooled to hand-warm, about 50C: hotter than that kills the enzymes, colder and they work too slowly.
3. Sprinkle 1 tbsp of plain flour over the warm mash and beat it in. Cover the pan with a lid or foil and stand it in an oven set to its lowest setting (about 50C), or in a warm water bath, for 4 hours. Stir every hour or so; the stiff mash will slacken to a loose, glossy, sweet-tasting purée. This sweetening step, imellys, is the whole point of the dish.