In a mixing bowl, beat butter with baking powder, salt, and cumin until creamy. Add masa harina and stir into butter mixture with a fork until the mixture is crumbly. Slowly add chicken broth, a half cup at a time, until mixture is still thick enough to form into dough, but not too soft. Divide dough and form into 12 balls.
Place each ball in the center of a prepared corn husk and spread out into a 3-4 inch square. Place about 2-3 tablespoons of chicken filling in the center of each square of masa dough. From one of the long edges of the corn husk, begin to roll tamale into a tube, making sure dough and filling are tucked inside of the corn husk. Using the corn husk ties, tie each end of the tamale close to the end of the filling inside. Double knot the ties. (Here I snipped off the excess ends of corn husks, leaving about a two-inch tail on either side of the ties.)
Place tamales on a French steamer in a large pot or in the steamer basket of a pot and fill the pot with water to just below the steamer basket. Cover pot with a tight-fitting lid. Bring water to boil, and then turn the heat down slightly to medium, and continue to steam tamales for 1.5 to 2 hours. Add water as needed, so the pot does not dry out. Can be cooked ahead of time, refrigerated, and reheated when ready to serve.