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 chicken 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 mixture resembles a thick cake batter, adding additional chicken stock, if needed. Add the baking powder and add salt, to taste, and whip for 1 to 2 minutes 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 are in the middle and narrow ends out. Spoon 1/4 cup of the masa batter into the center where the husks join and with the back of a spoon, spread it into a 4-inch square. Place about 1 generous tablespoon each of the duck, grated cheese, and chopped poblano in the center of the masa square.
Fold 1 side of the cornhusk 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 remaining corn husk, cover steamer with a tight fitting lid and steam for 1 1/2 hours, or until tender and tamale easily pulls away from corn husk. Allow tamales to rest for 10 to 15 minutes before serving.
Yield: about 18 tamales