Soak corn husks in warm water until soft and pliable. Set aside.
Cook chicken in lightly salted water until tender. Shred and reserve some broth.
Simmer tomatillos and green chiles until softened. Blend with onion, garlic, cilantro, and salt until smooth.
Cook the green sauce in a pan for 10 minutes, then stir in shredded chicken. Set aside.
In a large bowl, beat lard or shortening until fluffy. Mix in masa harina, baking powder, and salt.
Gradually add warm chicken broth and mix until the masa is soft and spreadable.
Spread a thin layer of masa onto the smooth side of a corn husk. Add green chicken filling down the center.
Fold sides inward and fold the bottom up to seal.
Stand tamales upright in a steamer and steam for 90 minutes, or until the masa pulls away easily from the husk.
Let tamales rest for 10 minutes before serving.