Soak the soybeans with the kombu seaweed for 12-24 hours.
Put 2 cups of soybeans in the blender, plus 4 cups of water.
Blend it very well.
Strain the mixture into a very large pan, using cotton or linen fabric.
With your hands, squeeze well the fabric until all the liquid comes out.
Do this repeatedly, using the same amounts, until there are no more soybeans left.
Cook the soy milk on low heat.
Mix the lemon juice with the salt apart and add it to the liquid. You’ll see it coagulating once it reaches 90ºC/194ºF, just before starting boiling.
When you see a clear separation between a transparent liquid and a thick white soft texture, it’s a sign that it’s ready and you can turn off the heat.
Put another piece of cotton or linen fabric on a strainer, and carefully drop parts of the tofu on it until you have nothing left.
Smooth the tofu with a spoon and put it in the fridge for no less than 24 hours, in order to get harder. Make sure you put a recipient under the strainer, that is capable of retaining the liquid that keeps coming out.
The longer you leave it in the fridge, the harder it will get. When you intend to use it, remove it carefully from the strainer and the fabric.