Briefly rinse the beans, then put them in a small saucepan.
Add enough water to cover the beans plus a few extra centimeters.
Put the pot on the stove over medium high heat and bring to a boil.
Boil briefly, then drain the beans using a fine-mesh sieve.
Put them back into the pot and add the same amount of fresh water again.
Keep simmering over medium low heat for about 90 minutes. Check in sometimes and top up with water to keep the beans submerged..
Once the beans are easy to squash between your fingers, they're ready.
Drain the beans again, but keep 125 ml (0.5 cup) of the cooking liquid.
Transfer them to a blender or food processor. Blend and add cooking liquid until you have a smooth and somewhat liquid paste. I usually all the reserved water. The paste will thicken again over the next steps.
Put the paste back into the pot and turn the heat to medium low.
Slowly add in the sugar and keep stirring until it is fully dissolved.
Keep going for a few minutes to let the paste thicken. Once you can draw a line at the bottom of the pot that doesn't close quickly, it's thick enough.
Stir in the salt.
Take it off the heat and store the paste in a bowl or food container. You can keep it in the fridge for a few days in a closed container.