In a medium bowl, soak the chiles in 2 cups warm water for 20 minutes. Drain, reserving the soaking water. In a blender, puree the chiles, 1/2 cup soaking water, garlic and cumin.
Meanwhile, in a medium bowl, mix 1 1/3 cups masa, 1 1/3 cups stock, 4 tsp. chili powder, the baking powder and 3/4 tsp. salt. In a large bowl, use an electric mixer to beat the butter on medium speed until fluffy, about 1 minute. Add the masa mixture; beat until smooth, 2 to 3 minutes. Add the stuffing; beat until a thick batter forms, about 1 minute (lumps may remain). Add more masa if too thin to spread; add more stock if too thick. Cover.
In a medium skillet, heat the oil over medium. Add the chile puree and 1 cup chile soaking water. Simmer, stirring often, until slightly reduced, about 8 minutes. Transfer 1/2 cup chile sauce to a medium saucepan; whisk in gravy and 2 tbsp. chili powder. Bring to a simmer, stirring often. Season with salt and more chili powder, if desired. Let cool; cover and chill.
Add the shredded turkey to the sauce in the skillet; simmer until warm, about 5 minutes. Season with salt.
Place each husk, concave side up, on a work surface, wide end facing you. Spread 1/4 cup dough across bottom third of husk, leaving a 1/2-inch border on each side. Spoon 1 tbsp. turkey filling onto the dough. Fold in the sides of the husk, applying pressure to encase the filling within the dough. Close the sides; fold the tapered end over so ends meet.
Nestle the tamales, open side up, in a steamer set over a pot of simmering water. Cover with a clean dish towel (fold the cloth so it doesn't hang over the sides), then with a lid. Steam until the dough no longer sticks to the husks, about 1 hour. Reheat the chili gravy; serve with the tamales.