Rinse the azuki beans and discard any broken bits.
Drain and transfer the drained azuki beans to a large pot.
Add enough water to cover the beans by 1–2 inches.
Place the pot on the stove and bring the water to a boil over medium-high heat.
Once boiling, drain the beans in a fine-mesh sieve.
Return the beans to the same pot.
Next, add more water to the pot to cover the beans by 1–2 inches.
Bring the water to a boil over medium-high heat.
Once boiling, put a lid over the beans.
Turn the heat to medium low and keep it simmering for the next 1–1½ hours.
Add more water to keep the beans covered, as needed.
After 1 hour, check if the beans are cooked. Pick up a bean and mash it with your fingers. When it mashes easily, it‘s done.
Drain the cooked azuki beans in a sieve.
Return the beans to the same pot.
Turn the heat to medium low and add half of the ¾–1 cup sugar.
Mix well.
Once the sugar has dissolved, add the rest.
Mix well, stirring constantly. Then, add ½ tsp kosher salt and stir.
Let the moisture evaporate.
When a line can be drawn on the bottom of the pot with a spatula, turn off the heat.
Transfer the anko to a flat baking sheet to let it cool completely.