In Sweden and Finland it is traditional to eat pea soup (‘hernekeitto’ in Finnish, ‘ärtsoppa’ in swedish’) on Thursdays, served with pork and mustard and followed with pancakes for dessert. In Finland the soup is made of green peas, in Sweden yellow. The tradition of eating pea soup and pancakes on Thursdays is said to originate in the pre-Reformation era, as preparation for fasting on Friday.
Scandinavian pea soup normally includes pieces of pork – although it may sometimes be served on the side – and a typical recipe would also include some onion and herbs such as thyme and marjoram. It is usually eaten with some mustard, often accompanied by crisp bread and often with the sweet liquor punsch (flaggpunch, served hot). Mustard is an important part of the dish, but the soup is served without it so that diners can stir it in to taste. The soup is then normally followed by pancakes with jam (strawberry, raspberry, blueberry, cloudberry or similar) which are regarded more as part of the meal than as a dessert.
Just add half the tin of water and bring to the boil.