Clean the soy beans with water and place them in a large bowl. Add enough water to rise up to 2-inch above the soybeans. This will ensure all beans are covered with water. Soak overnight or up to 8 hours.
The next day, set a nut milk bag over a large bowl. Then, drain out the soaked soybeans and transfer them to a high-speed blender.
For each cup of soaked soybeans, add 2½ to 3 cups of filtered water to it. Blend at medium speed for about 2-3 minutes until the nuts are broken down into fine meal. Blend in batches if needed.
Empty it to the nut milk bag. Squeeze out as much liquid as possible. Alternatively, strain the liquid over a fine-mesh twice to make sure there is no soy pulp in the liquid.
Pour this liquid into a tall non-stick skillet (I used a 12-inch skillet) and turn on the heat. Set it at medium heat and as soon as it reaches to barely boil, turn the heat to medium low and maintain the heat between 212-225F. Scoop up the foam with a skimmer. You may still see wisps of smoke from the pan but the mixture is not boiling nor simmering.
After 3-4 minutes, a thin layer is formed at the top of the soy milk. The layer looks wrinkly and the outer perimeter sticks to the side of the pan.
To remove the sheet, gently loosen the side with a wooden skewer. Then, use the same wooden skewer and gently push the skin to one side and lift it up. Immediately transfer to a parchment paper. Repeat the process until you can't get any layer at the top.
Store in an airtight container or let them dry at room temperature. Check notes below for other ways to dry the tofu skins.