Lingonberries are everywhere in Finland, growing in clumps on small bushes. They make a tart, sourish jam that is delicious served with meats and game; try it with your Christmas turkey or alongside a baked ham. Make it in a heavy-based saucepan suitable for making jam. You might need to adjust the amount of sugar, depending on the tartness of your berries. The jam will be ready to eat once it has cooled, but you can also seal it in jars (while still hot) and store for when you need it.