In the making of the traditional Finnish sweetened potato casserole, wheat flour is added to warm, mashed potatoes and the mixture is left to stand in a warm place for several hours.

During this time, the amylase in the flour will start to break down the potatoes' starch into sugars, sweetening the dish. The ideal temperature for this sweetening process is between 55 and 75 °C. If the temperature exceeds 75 - 80 °C, the process will be stopped, due to the breakdown of the amylase molecules.

This traditional way of making the casserole will take several hours, so instead of waiting for the mixture to sweeten naturally, one can cut corners by just adding a little dark molasses to the batter. This method is highly disapproved by the potato casserole purists, though :-)

The potatoes used in this recipe must be floury, because their starch content is higher than that of waxy potatoes. Best result is gained when using late autumn and early winter potato varieties. New potatoes and the like should never be used.

Traditional way of making potato casserole:

1 kg floury winter potatoes
about 500 ml water for cooking (or enough to just cover the potatoes)
2 tbsp flour
25 g butter
about 400 ml whole milk
about 1 tsp salt

Under running water, brush the potatoes clean, but do not peel them. Cook the potatoes in unsalted water until tender. Save some of the cooking liquid. Place the uncovered pan back to the warm stove plate so that the excess moisture will evaporate, and the potatoes feel dry. Using protective gloves, peel the hot potatoes and puree them using a food mill. Work quickly, as the mixture must not cool too much. The ideal temperature is between 55 and 75 °C.

Add some of the reserved hot cooking liquid in the puree, especially if it is very dry. Note that the potato mixture will turn considerably runnier during the sweetening process, so do not add too much liquid either. While the puree is still hot (55 - 75 °C), sprinkle the flour on top of it and mix it in. Cover the dish tightly with a lid or a piece of foil and place to sweeten in a warm place, like in a cool oven (about 60 - 70 °C). Since it is vital to keep the temperature stable, it is best to monitor it by using a reliable thermometer (eg a digital meat thermometer).

Let the potato puree stand overnight in the warm oven, mixing it a few times. When the mixture has turned slightly sweet and is runnier, it is ready to be baked. Melt the butter and mix it in the potato puree together with the salt. Stir in enough milk until the puree has the consistency of a runny porridge or a thick gruel. You may need more milk than stated in the recipe.

Pour the batter into one or two buttered oven casseroles. Make sure you fill the dishes only halfway as the batter will rise and bubble during baking. Bake the casseroles either at 150 - 175 °C for about 2 to 3 hours, or overnight (about 8 hours) at 80 - 90 °C, until the batter has thickened and nicely caramelized on top. The longer cooking time at a lower temperature will give a better result.

The sweetened potato casserole is best when eaten straight from the oven. The batter can be frozen before baking, although this will somewhat worsen its consistency. Let the frozen casserole thaw in refrigerator, then bake it as described above.

Recipe source: adapted from traditional Finnish recipes.

Quick way of making potato casserole:

1 kg floury potatoes
about 500 ml water for cooking (or enough to just cover the potatoes)
50 ml flour
50 - 100 ml dark molasses
500 ml milk
about 1 tsp salt

Brush the potatoes clean, but do not peel them. Cook the potatoes in unsalted water until tender. Pour out the cooking water. Place the uncovered pan back to the warm stove plate so that the excess moisture will evaporate, and the potatoes feel dry. Using protective gloves, peel and puree the hot potatoes with a food mill and mix with the rest of the ingredients.

Pour the batter into one or two buttered oven casseroles. Make sure you fill the dishes only halfway, the batter will rise and bubble during baking. Bake the casseroles either at 150 - 175 °C for about 2 to 3 hours, or overnight (about 8 hours) at 80 - 90 °C, until the batter has thickened and nicely caramelized on top. The longer cooking time at a lower temperature will give a better result.

The sweetened potato casserole is best when eaten straight from the oven. The batter can be frozen before baking, although this will somewhat worsen its consistency. Let the frozen casserole thaw in refrigerator, then bake it as described above.

Recipe source: family recipe.