A Finnish Christmas table traditionally has been crowned by several different kinds of bakes (casseroles in US English) depending on where in Finland we are talking about. There are regional differences and some may have fallen on the wayside and now these three remain: carrot, swede and potato. But the greatest of these is potato.

The smelliest is the swede.

And the one no one cares either way about is the carrot bake. It's like the Lady Edith of Christmas bakes, a thoroughly uninteresting character with uninteresting suitors, who go missing without no one giving a damn. Potato is obviously the shiny, pretty and lovable Lady Sybil and swede is Lady Mary who's got a definite nasty whiff about her, but who you couldn't have Downton Abbey without.

The dish is called sweetened potato bake. Potatoes are first boiled and then mashed. Then they are sweetened in the oven. You mix in a little bit of plain flour, cover the pan and put it in the oven. Then the magical Christmas oven fairies turn the mash into a shiny golden sweet gorgeousness. Or maybe it's the enzyme amylase in the flour that reacts with the starch of the potato. Either or.

You can use golden syrup for added sweetness if the natural process won't quite do it. The temperature is key, if your oven is unreliable and the temperature is wrong the sweetening won't happen, you need to keep it above 55C and below 75C at all times. But even then sometimes the potatoes are just recalcitrant, so there is no shame in a squirt of syrup.

The bake is enjoyed hot fresh from the oven with different types of fish like gravadlax of course, hot smoked salmon, gravad whitefish, pickled herring and baltic herring. And it's not all fish, there is always also a massive ham, which is salted in brine for several days and then baked overnight in low heat until "overdone". Then it's dressed with mustard and whole cloves and baked until nicely browned on the outside.

This potato bake takes all day, the potato mash requires several hours of "sweetening" in the oven. Before you season it and bake it for several hours. Little active prep time, but lots of hanging around the oven and drinking mulled wine singing carols time.

Finnish sweetened potato bake (will make a lot - I made half a portion)

2 1/2 kg potatoes (floury: King Edward or Maris Piper)
1/3 cup plain flour
2 cups milk
Salt
1 tsp nutmeg
3-4 tbsp golden syrup
Butter

Peel and wash potatoes (the most traditional recipes recommend boiling them unpeeled and then peeling them hot, but that's really such a pain that I can't be bothered, if you want to do it, go for it and good luck to you and your thumb). Boil the potatoes in unsalted water until well done. Drain the potatoes preserving the water and mash the potatoes.

Cool the mash until it's little warmer than lukewarm (about 60C). Add about half a cup or a bit more of the preserved cooking water and mix.

The mask should be 55-75C, otherwise the sweetening won't happen, so make sure you cool it down to right temperature and that you oven is between 55 and 75C, ideally around 60C. You can also do this bit in a warm water bath, but I don't know how you would control the temperature so I always do it in the oven.

Once you think your mash is the right temperature mix in half of the flour. Cover the pan and place in the 60C oven.  After half an hour mix in the rest of the flour and leave in the oven for minimum 4-5 hours, but the sweetening process can take up to 8 hours. You don't want to disturb the potatoes a lot during this time. The potatoes are ready when the mash has loosened and become shiny and sweet.

When you are happy with the potato mix add enough milk to make a smooth loose porridge-like mix. It should be thinner than porridge but thicker than soup. Add the nutmeg and season with salt. If it is not sweet enough add some syrup.

Butter one or more baking dishes and fill each a little more than half way with the potato mix. The potato will bubble while baking, so it's important not to overfill. Add a couple of knobs of butter on top.

(If you want to serve the bakes later, you can refrigerate or freeze them at this stage and do the final baking just before you want to serve them.)

Bake in 150C for 2 hours and serve hot.