To make anko from scratch, you need azuki beans, water, sugar and salt. Start by boiling the beans in water until they are soft and mashable. Sweeten with sugar to taste with a bit of salt to balance the flavour. Continue to boil until the bean mixture reduces to a thick paste. Strain any remaining liquids. You want a paste that's thick but firm at room temperature, not runny like a liquid. If you want a thick, chunky paste (tsubuan), mash the paste with a spoon, leaving some beans and skins intact. Alternatively, you can turn the paste into a fine and smooth texture (koshian) by processing in a blender.