For the corn husks - Rinse the corn husks well. Place the husks into a deep bowl or Dutch oven. Add enough water to cover the husks. Place something heavy over the husks to press them down into the water. Allow the husk to soak or 2 to 5 hours
For the masa - In a large bowl, add the corn masa harina, salt, and baking powder. Whisk together until blended. Add the oil to the masa and blend until completely mixed. The texture will be like damp sand. Pour the reserved cooking liquid from the pork in until completely mixed. Add the chicken broth about 1 cup at a time until it's like peanut butter.
For pulled pork - Place the pork into an electric pressure cooker. Add the water, onion, and seasonings in Press high pressure cook setting for 50 minutes. When done allow the pressure to naturally release. Remove the pork and shred it with two forks. Reserve one cup of the broth, skimmed, to use in the masa.
For the sauce: - Pour 2 cups of chicken broth and the other ingredients for the sauce into a medium saucepan. Bring them o a boil over medium high heat. Reduce the heat to low, cover the pot, and simmer for 10 minutes until the chilies are softened. Transfer to a blender and blend on high for 2 to 3 minutes or until the ingredients are completely puréed. If the sauce is not thin enough add more chicken broth.
Assemble - Drain the corn husks. Working with one husk at a time, spread about ¼ cup of the masa mixture over the wide end of the corn husk, covering about ⅔ of the husk. Spoon 1 to 2 tablespoons of the pork filling in the middle of the corn masa. Fold the tamale by bringing the sides over the filling, overlapping the edges. then, bend the bottom tip, folding upwards.
Steam - Add 1.5 cups of water into pressure cooker. Put a steamer basket into the bottom. Stand the prepared tamales vertically in the basket. Seal the lid and steam valve shut. Set to high pressure for 10 minutes. Perform a quick release of the pressure when done. Let the tamales rest for 10 to 15 minutes.
Serve - Remove husks, pour sauce over the top and serve.