Preparing the uchepos: Cut through each corncob at the thickest part, just above the base. Unwrap the leaves very carefully, trying to keep them whole, and trim off the points. Rinse the leaves and set them aside to drain.
Cut the kernels from the cobs as near to the core as possible. You should have 4 cups of kernels.
Put the kernels into the blender with the water and salt and grind them until they are very smooth. It will be much easier to do in 2 lots. You will have to keep stopping the blender and releasing the blades; but do not add more water.
Making the uchepos: Smear a thin coating of the corn mixture over the broadest part of the cornhusk, allowing for turning down about 1 1/2-inches at the bottom broad part of the husk and about 3-inches high at the pointed top. Fold the sides of the husk together firmly. Turn up the pointed end of the leaf and fold the broader over it.
Cooking the uchepos: The most convenient way to cook uchepos is with a conventional steamer. Fill the bottom of the steamer with water up to the level indicated and bring it to a boil. Line the top of the steamer with cornhusks, covering the bottom and sides well. Stack the uchepos upright. For the best results, they should be packed firmly but not too tightly, because the husks swell out as the dough cooks.
Cover the uchepos with more cornhusks. Cover the top of the steamer with a thick cloth ¿ a piece of old toweling is best ¿ to absorb the condensation from the lid of the steamer. Cover the steamer with a tightly fitting lid.
As the water in the bottom part comes to a boil, put a coin into it, put the top part of the steamer on, and let the uchepos cook for about 2 1/2 to 3 hours over a medium flame. Keep the water bubbling, but not boiling violently. That is the reason for the coin. You will be able to hear it dancing about, and it will tell you if the water goes off the boil or is getting dangerously low. It the water is allowed to go off the boil the uchepos will be heavy. Keep a kettle of water simmering so that you can refill the steamer when necessary.
To test the uchepos for doneness, remove 1 from the center, and 1 from the side of the steamer. As you open the husks, the dough should come away easily from the husks and be completely smooth. To make doubly sure, open up the uchepos and see if they are spongy and well cooked throughout.
Recipe excerpted from The Cuisines of Mexico by Diana Kennedy: Harper and Row, Publishers, Inc., 1972