Place a steamer basket in a large pot filled with a couple of inches of water (so the water is below the basket). This might take 1-2 pots, depending on the size of the pots. Line the basket with a few corn husks. Place the tamales into the pot upright, so the thinnest part of the corn husk is at the bottom. Place a few corn husks on top. Drape a damp kitchen towel over the pot and close the lid. Steam for about 90 minutes, checking to make sure the water in the pot doesn't run dry. To test for doneness, take a sacrificial large tamale from the pot and open it up. The masa should not be sticky and should be cooked evenly. If not, return it to the top and continue steaming.