Soak the soy beans with cold water at least for 4 hours until the beans can be easily broken. This step is extremely important to make sure the soy milk is thick enough.
Then transfer to blender and blend until really smooth. You can finish in batches . Then strain the pulp out and get pure soy milk.
Heat the soy milk with high fire at first and remove the bubbles after boiling. Then slow down the fire and keep the soy milk hot (reaching simmer) but not boiling. Wait for 5-8 mins until the skin formed. You can watch it on surface via the wrinkles. Use a knife to separate the tofu skin with the edges of the pot. Then start with the thicker edge to pick the skin out.
Transfer to a baking grill for cooling down. You can use it directly or dried with sun or fan.