Wash the beans and place into a large pot with water and bring to boil over medium high heat.
Once boiling, Reduce the heat to medium and let it simmer for about 1 to 1.5 hour, Adding more water as needed until the beans are soft and you can mash it with your fingers.
Drain the beans and discard the water.
Smash the beans until you get the desired texture you want or use a food processor if you want a fine paste sweet red bean.
Over medium heat, Transfer the paste, sugar, vanilla and salt into a saucepan. Stir the paste constinously until sugar melts and the paste has thickened.
When you can draw a line in the bottom of the pot and it holds for 1 or 2 seconds.the paste are done, turn off the heat.
Let it cool and store the paste in an airtight container for a week in the refrigerator or 1 month in the freezer.