Place the mung beans into a large container and cover with several centimetres of cool water; let stand 3 hours to overnight. Drain and rinse before using.
Combine the beans with the water in a large saucepan over medium heat; cook until the beans are tender, about 30 minutes. Stir the sugar into the mixture; cook and stir until the sugar is completely dissolved. Remove from heat and serve warm.
If palm sugar is unavailable, substitute in dark brown soft sugar.