Place beans in a saucepan and cover with 2 cups water; bring to a boil and cook for 5 minutes.
Drain beans and transfer to a clean saucepan.
Cover with 2 to 3 cups water and bring to a boil. Reduce the heat to low, cover, and simmer, adding more water as needed, until beans are soft and can be crushed between your fingers, 1 1/2 to 2 hours.
Drain beans and return to the saucepan. Add sugar and set over medium-high heat.
Cook, stirring constantly, until sugar melts and beans form a loose, shiny paste, about 10 minutes.
Immediately transfer paste to a container to cool.