Combine the corn husks and enough water to cover in a medium saucepan and bring to a boil. Top the husks with a heavy plate or bowl to keep them submerged, and boil for 10 minutes. Remove the pan from the heat and steep until the husks are soft and pliable, 1 to 1 1/2 hours. Drain the husks, remove any corn silk, and pat dry before assembling the tamales.

Process the grits in the bowl of a food processor for 1 minute. Bring the chicken stock to a low boil in a small saucepan. Transfer the grits to a large bowl and add the hot stock. Let stand, uncovered, for 10 to 12 minutes. Add the masa harina and cumin and mix until evenly combined. Cool to room temperature before proceeding.

In the bowl of an electric mixer fitted with the paddle attachment, whip the lard until smooth, light, and creamy, about 2 minutes. Stir in half of the masa mixture and whip until well blended. Add the remaining masa mixture, little by little, until the batter resembles thick cake batter, adding additional chicken stock if needed. Add the baking powder and salt and whip for 1 to 2 minutes, or until well incorporated and smooth.

Lay 1 corn husk on a work surface with the narrow end closest to you. Top with a second corn husk so that the fat ends overlap in the middle and the narrow ends point in opposite directions. Spoon 1/4 cup of the masa batter into the center of the husks and, with the back of a spoon, spread it into a 4-inch square. Place about 1 generous tablespoon each of the chicken, grated cheese, and chopped poblanos in the center of the masa square.

Fold 1 side of the corn husk over the filling, fold the other side over the filling, and then the top and bottom ends. With a piece of kitchen string or a thin strip of leftover corn husk, tie the tamale together loosely so that it resembles an oblong rectangular package. Repeat with the remaining corn husks and filling.

Once the tamales are assembled, line a steamer basket with any remaining corn husks and layer the tamales inside the steamer basket, leaving enough room for the tamales to expand slightly while cooking. Cover the tamales with another corn husk, cover the steamer with a tight-fitting lid and steam for 1 1/2 hours, or until the tamales are tender and pull away easily from the corn husks. Let sit for 10 to 15 minutes before serving.