For the red tamale sauce: Add the ancho chiles, California chiles, onions and garlic to 4 cups boiling water. Turn off and let rest for 30 minutes. Process until smooth in a food processor or a blender (including the water).
Heat oil in a soup pot, then add cumin and oregano. Cook, stirring, until fragrant. Add pureed chiles, vegetable stock, sugar and salt and let simmer, 10 minutes. Add can of red chili sauce and stir to heat thoroughly.
For the filling: Pour oil into a saucepan over medium heat. Add the mushrooms, squash, garlic, oregano and some salt. Cook, stirring, until the vegetables are glazed and no longer crisp, approximately 10 minutes. (The filling does not need to be tender because it will also cook while tamales are steaming.)
Add 3/4 cup red tamale sauce to the filling and let cool.
For the masa: Mix together masa, baking powder and salt in a large bowl until incorporated. Stir in the vegetable stock and 1/2 cup red tamale sauce.
Beat the vegetable shortening in a stand mixer until fluffy, then beat in masa mixture with the mixer running until evenly incorporated.
Soak the corn husks in hot water until softened and pliable, about 15 minutes. Drain and squeeze water from husks.
Spread masa on the less ridged side of a corn husk, across all but the pointed end, with a spatula or the back of a spoon, Fill each with 2 to 3 tablespoons squash and mushroom mixture.
Roll tamale by folding one long side about a third of the way over the filling, then the other side, and folding the long pointed end against the tamale (this will leave the filling exposed on the opposite end, and that is okay). Push two black olives into masa on the open end of each tamale.
Place a steamer rack in a large pot filled with just enough water so the bottom of the rack sits just above the water line. Line the rack with flat corn husks. Place rolled tamales in pot on the rack, open-side up. Drop two pennies in the bottom of the pot. Cover the tamales with more flat husks. Cover the rack with a clean dish towel. Cover the large pot with a tight fitting lid or aluminum foil and steam for approximately 1 hour and 30 minutes. (The pennies will dance and tinkle furiously when the water comes to a boil. Turn the heat down until the pennies dance to a relaxing beat. If you no longer hear the pennies, you have boiled away the water, and you had better add more?fast!)
Serve tamales with additional red tamale sauce.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.