Homemade soy milk is the key to the best tofu (most store-bought versions won't work), but the origin of the soybeans isn't an issue: "I asked tofu makers in Kyoto, Japan, where their beans are from," says Keane, "and they said America."
For details on making freshly pressed soy milk from dried soybeans, refer to steps 1-4 of Keane's Tofu Skins, Silken Tofu, or Firm Tofu recipes.
Tofu skin, known as yuba in Japan, forms on the surface of hot soy milk, similar to the skin that develops on warm cow's milk. When the skin is fully formed, use a paring knife to carefully detach it from the side of the saucepan. Carefully slide a chopstick or skewer under the skin and lift it from the milk. Let drain for a few seconds before transferring to a plate.
To set the curd of this delicate tofu—delicious, even plain—combine freshly made hot soy milk with sea salts such as magnesium chloride. The sea salts (nigari) coagulate the proteins in the milk, forming very fragile, custardy curds.