Step 1Soak the corn husks: Fill a large bowl or sink with hot water and soak the dry husks until soft, 45 minutes. Drain and rinse well.
Step 2Cook the filling: Cut the squash in half lengthwise, remove the seeds and strings, and wrap well with plastic wrap. Cook in a microwave on high until soft, 15 to 20 minutes.
Step 3Make the sauce: In a sauce pan over medium heat, heat the oil. Add the guajillo, pasilla and chiles de arbol, bay leaf and garlic. Lightly toast until fragrant and starting to color, 2 to 3 minutes. Add the sesame seeds, pumpkin seeds, allspice and clove, and toast until the seeds begin to color, about 3 more minutes. Add the broth, along with the tomatillos, tomatoes and salt and simmer until the tomatoes have broken down, about 10 minutes. Remove from the heat and carefully pour into a blender jar or the work bowl of a food processor. Make sure to get everything in there (including the bay leaves). Blend until smooth and set aside. This makes about 3 cups of sauce.
Step 4Prepare the filling: While the sauce is cooking, cut the cheese and squash into rectangular pieces about 3 inches long, 1 inch wide and 1/4- to 1/2-inch high. (I like to put in fat little slices so that you really taste the cheese and squash.)
Step 5Assemble the tamales: Lay a single husk on a work surface and, using a small spatula or the back of a spoon, smear about 3 tablespoons of masa across and about halfway down the husk, depending on the size of the husk. (You don't want it to be too thin because then it will taste like a dried-out tortilla chip, but if you add too much, it's gross.) It should have a thickness of about 1/4-inch. Add one piece each of the squash and the cheese. Top with about a tablespoon of sauce. Fold once across, give it a little pinch, and then fold the other side over it. The opposite side will act as glue. Squeeze toward the tip and fold the bottom, empty part of the husk up. Repeat with the remaining husks and filling.
Step 6Steam the tamales: Place a steamer basket into a large pot and stand the tamales together (but not too tightly) in the basket so that the open part of each tamale is upright in the pan. Lightly cover the tamales with damp kitchen towels, a double layer of food-safe plastic wrap and a double layer of foil. (A helpful trick is to shape two eyes and a smiley mouth with leftover masa and lay them on the foil. The masa will cook on top of the foil and become firm when the tamales are done.) Steam the tamales on the stove-top until the masa is cooked through, about 45 minutes.
Step 7Serve with sauce.