Place corn husks in a large stockpot or pan and cover completely with warm water. Allow to soak for at least 30 minutes or until softened.
While corn husks are soaking, in a large bowl mix together masa harina, salt, baking powder, and whisk to combine. Add oil, beat until combined, then gradually add stock and continue beating until mixture is fluffy, about 10 minutes.
Lay soaked corn husks on a flat surface. Spread about ¼ cup masa mixture into thin layer over half of husk. Add 2-3 tablespoons filling to tamale, then fold husk over to surround filling in masa. Then fold lengthwise. Repeat until filling or masa mixture is used up.
Place tamales in steamer, and steam for 30 minutes to an hour and a half, until husks open cleanly.