Rinse the black soybeans thoroughly and soak them in water for at least 8 hours.
Put the soaked black soybeans and water into a blender and blend until smooth.
Strain the mixture to separate the skins and obtain smooth soy milk.
Pour the strained soy milk into a pot and simmer over medium heat for 10 minutes, stirring constantly.
Season lightly with salt or sugar according to your preference.
Pour the finished black soybean soy milk into a cup and enjoy.