Gather all the ingredients.

Put 1½ cups azuki beans in a strainer and place it inside a large bowl. Rinse the azuki beans in running water until the water is clear. Discard any pieces that are floating. Drain the water.

Transfer the beans to your stovetop pressure cooker or the inner pot of an Instant Pot. Next, add 5 cups water to the pot.

Cover and lock the lid of your pressure cooker. If you’re using an Instant Pot, turn it on and press the Bean/Chili button. Press the 'minus' button to decrease the cooking time to 25 minutes from the default 35-minute cooking time.

Before you walk away, make sure the steam release handle points at Sealing and not Venting.

If you’re using a stovetop pressure cooker, cook on high heat until you reach high pressure. Then, reduce the heat to low to maintain the pressure for about 20 minutes.

When it’s done cooking, the Instant Pot will switch automatically to the Keep Warm mode. Let the pressure slowly release by itself for 15–20 minutes.

If you are using a stovetop pressure cooker, remove the pot from the heat, and let the pressure release naturally. Before opening the lid, turn the steam release handle to Vent and release any remaining pressure.

Skim the foam off the surface and discard. Pick up one bean and mash it with your fingers. If it mashes easily, it‘s done. If the beans are still not done, close the lid and cook again under high pressure for a few more minutes.

If you‘re making Zenzai or Oshiruko (Red Bean Soup), DO NOT DRAIN and continue to the next step with the cooking liquid remaining in the pot. To make Anko, drain the azuki beans through a fine-mesh sieve and put the azuki beans back in the inner pot.

Next, add 1¼ cups sugar to the pot. Press the Sauté button and select the Low option.

Let the sugar dissolve completely, stirring occasionally with a wooden spoon. Then, add ⅛ tsp Diamond Crystal kosher salt.

Continue cooking as you let the moisture evaporate. When you can draw a line through the azuki bean mixture and see the bottom of the pot for 1 second, turn off the heat.

Take out the inner bowl from the Instant Pot and let the mixture cool for 5–10 minutes.

After 5–10 minutes of cooling, transfer the azuki beans into a food processor or blender. Fill it only halfway and work in 2–3 smaller batches, if necessary.

Run the food processor or blender until the mixture becomes a smooth texture. Transfer to an airtight container.

When it has cooled and thickened more, the koshian is now ready to use in a variety of Japanese sweets.

To store, cover and store in the refrigerator for up to 4 days and in the freezer for up to a month.