Wash Jeju soybeans thoroughly and soak them in water for about 6 hours.
Boil the soaked soybeans in boiling water for 15 minutes.
Remove the skins from the boiled soybeans.
In a blender, blend the boiled soybeans with water and salt until smooth to make soy milk.
In a cup, mix Jeju soy milk, milk, and syrup well.
Add ice to serve cold.