Soak dried chilies in hot water, in a large ziploc bag for 15 minutes (or as long as it takes to cut up onion and meat)
Trim fat off of pork shoulder and place in a large crock pot
Cut up onion into large chunks (in 8ths)
Carefully, take chilies and working over the bag of water, pull off tops and rinse the seeds out. Place whole chilies in the with meat (I push the chilies down in between the meat), do the same with the onion. Then add about two cups of the chili water, that has been strained.
The meat will need to cook all day or over night, at least 12 hours. During the cooking, take the excess juices out and set to the side DO NOT THROW AWAY. I would suggest you put a sheet pan under the crock pot, in case the juices spill over while you are away from it.
Pull meat from crock pot leaving the drippings behind. Put the meat in a large ziploc, strain the drippings into a large bowl, you don't want any of the chili skins they are uneatable. Let them both completely cool in the fridge. (You don't have to do this step, BUT it makes it easier to work with)
DAY TWO: Reheat the meat drippings adding chili powder, garlic and cumin. Pull meat from bag and shred into a large stock pot over medium heat, adding about 2 cups of meat drippings and stirring so it won't burn, if you'd like add about 1/4 cup of canola oil. Once it has heated through pull it off the heat.
TO MAKE THE MASA: In a LARGE bowl or tub (you have to have lots of mixing room) empty the entire contents of the Maseca. Add paprika, garlic, cumin, and chili powder, mix well so that there are no "pockets" of spices. Add the oil (4 cups) and mix WELL. While mixing add the rest of the meat drippings, should be about 3-4 cups. You are looking for a thick peanut butter consistency, should not look "dry" at all. If you need more liquid (which you probably will) add the chicken broth, 1 cup at a time until you reach a good consistency. Let it sit for 10-15 minutes while you soak the corn husks. Corn husks should be soaked in hot water (usually in my sink, weighted down with something to keep them under water)
TO ASSEMBLE: With an ice cream scoop for the masa, and a small tablespoon scoop for the meat, take a corn husk and on the SMOOTH side (one side will have ridges) lightly dab with a paper towel.
Take a scoop of masa and place it in the middle of the wide edge of the husk. Pressing down with your hands, spread the masa till its about 1/4 inch thick, 1/4 inch from the edge and 1 inch from each side.
Take two scoops of meat and place in the center of the masa. Working from the edge closest to you, roll the masa over the meat, making sure that the husk does not get under the masa, so masa and meat should be touching. Roll and fold the narrow end of the husk towards the top. Place the tamale open end up in a steamer. Repeat...repeat....repeat.
Steam tamales for 2 hours with lid on. Keep an eye on the water level.