Place tomatillos, onion, cilantro, garlic, ½ teaspoon salt, 1 teaspoon chicken bouillon granules in a blender (this might take two batches, depending on blender capacity). Blend on high until smooth (if needed add 1 to 2 tablespoons water to ease blending). Heat the oil in a 3-qt container over medium high heat. Place the salsa in the container and cook until it turns a deeper green and reduces by ¼ (it should be thick). Mix the cooked shredded chicken with 1 1/4 cups salsa. Set aside the remaining salsa for serving once the tamales are cooked and ready to be served. Pull 1/4-inch strings from reserved husks to wrap the tamales (or use twine) and set aside. Cover the corn husks (including the pulled strings) with warm water and let stand until pliable (at least 30 minutes). Meanwhile, in a large bowl, mix 2 cups of the broth, masa, lard, 1 teaspoon salt, ½ teaspoon chicken bouillon granules, and baking powder. Beat with an electric mixer until well combined, adding the remaining chicken broth as needed to make a soft dough (the dough should be moist, but not sticky). Drain the corn husks and pat dry with paper towels. Place 3 level tablespoons of dough on each corn husk. Slightly spread the dough out, making an indentation in the center with the back of a spoon. Place about 1 tablespoon of chicken tomatillo mix on the center of the dough and fold dough around filling (if corn husks are too small, overlap 2 husks). Fold the bottom one-third of the corn husk over the filling and fold the sides in towards the center. Tie the tops with corn husk strings (or twine). In a 10 to 12-quart tamales steamer, pour boiling water under the steamer insert, almost touching it (the water should not touch the tamales when they are added). Stand the tamales inside pot, leaning against the sides all around. Cover and reduce the heat to medium. Simmer gently for 1 hour to 1 hour 15 minutes or until the tamale dough becomes firm. Add more water if needed during cooking time. Let stand uncovered for 10 to 15 minutes. Carefully unfold each tamale by removing the string and opening the husk. To serve, carefully open the tamales and top with the remaining warm tomatillo salsa and a dollop of sour cream.