The traditional way of making one of the Finnish Christmas staples. Flour is added to warm, mashed potatoes and the mixture left to stand in a warm place for several hours. The amylase in the flour begins to break down the potato starch into sugars, sweetening the dish. Now, try as I might, I can never get it to work well enough and have to resort to the modern way of adding treacle!! So, I'm listing it as an optional ingredient!