How to Make It
In a saucepan, cover the pork with the water and add 1 1/2 teaspoons of salt. Bring to a boil, then cover partially and simmer over low heat until the pork is very tender, about 2 hours. Transfer to a plate; cover with a damp cloth and let cool.
Strain the cooking liquid and return it to the saucepan; skim off the fat. Add the onion, garlic, anchos, tomatoes and tortillas. Bring to a boil and simmer for 30 minutes. Let cool to room temperature.
In a skillet, toast the pumpkin seeds over moderate heat until puffed, about 3 minutes. Puree the ancho mixture with the pumpkin seeds in batches. Return the puree to the saucepan and simmer over moderate heat, stirring, until slightly thickened, about 10 minutes. Season with salt.
In a bowl, combine the grits, masa harina and 1 1/2 teaspoons salt. In a saucepan, bring the chicken stock to a simmer. Slowly stir in the grits and masa harina. Cover and cook over low heat for 30 minutes, stirring. Add the butter, season with salt and let the dough cool slightly.
Meanwhile, soak the corn husks in water until pliable, about 20 minutes; drain. Shred the pork into a bowl and stir in 3/4 cup of the ancho sauce; season with salt.
Spread a corn husk on a work surface. Spread 3 tablespoons of the warm tamale dough over the wide end of the husk to form a 1/4-inch-thick rectangle. Spoon 1 heaping tablespoon of the pork filling in the center of the dough. Using the husk, bring the dough up to enclose the meat. Fold the husk around the dough and fold the narrow end of the husk under the tamale. Repeat with the remaining husks, dough and pork filling; rewarm the dough in the microwave oven or on a plate in a steamer if it cools down.
Cook the tamales in a large steamer until heated through and firm to the touch, about 15 minutes. Transfer to a platter. Rewarm the remaining ancho sauce and serve with the tamales.