Soak the adzuki beans in plenty of water. When the beans have swelled, boil over medium heat.
Bring to a boil and drain (to remove bitterness). Add plenty of fresh water and cook over medium heat again. Turn the heat off after about 10 minutes, and leave to cool down.
When the beans have cooled down, bring up to a boil once more, then cool down again. If the beans have split open, they're done. If they are still hard, repeat boiling and cooling procedure until tender.
When the beans are tender, add sugar and cook over medium heat. Mix and mash the beans with a spatula. Add the salt.
If you can write an "S" on the bottom of the pan with your spatula, turn off the heat. To use the anko in anpan (anko filled buns), dry it off well to make it rather firm.
Divide the anko into 30g balls. For ohagi, divide into 50 balls. You can freeze the anko.
Story Behind this Recipe
If you make your own anko, you can adjust the sweetness to your taste. It's also preservative-free, so I like it.
There's no need to cook the beans for 1 to 2 hours. Just repeat the boil-simmer and cool steps, and you'll end up with tender and plump cooked beans. Use a pan with a thick bottom. If you use the same amount of sugar as the beans, the anko will be not that sweet. Please adjust the amount of sugar to taste.