1) Cover beans with cold, soft water and soak overnight.
2) On the next day, in a pressure cooker, cook the beans in the liquid for 20 minutes or steam in a steamer until soft.
3) Rub sauce through a strainer or liquidize using a blender.
4) Add in beans and sultanas and cook for 15-30 minutes over low heat.
5) Season with salt and pour in lemon juice to taste.