Soak the mung beans until they are soft. You can soak them overnight to cook in the morning. If using split mung beans with skins, soak overnight and remove the skins.

Soak the tapioca pearls for about 30 minutes.

Cook the mung beans until soft (about 30 minutes for a smooth texture, though they are cooked after 15 minutes). Stir well and mash the beans more if desired. Add sugar to taste. Cook over medium heat to prevent boiling over, as the starch can cause it to foam up.

Add the soaked tapioca pearls and cook over low heat, stirring constantly to prevent sticking. Cook for another 5 minutes, or until the tapioca pearls are translucent, then remove from heat.

Serve in bowls. This mung bean sweet soup is delicious with coconut milk.