Prep Banana Leaves - Remove banana leaves from package, unfold and wipe clean with a damp cloth. Cut each into 12 by 10-inch rectangles. Cut enough kitchen twine to have one long one and 2 shorter ones per tamale. These will be used to tie the tamales with 2 around the middle and the longer one tying the wider way. Set everything aside.
Make Shredded Turkey - Place turkey pieces in a medium saucepan (chicken thighs can be used) along with salt, onion, garlic, and peppercorns. Cover with warm water and bring to a boil. Reduce heat to medium-low and simmer, partially covered, until the meat is falling off the bones. About 35 to 40 minutes. Remove turkey from water and let cool enough to handle. Remove skin and tear meat until long shreds. Set aside.
Heat mole to a boil over medium-high heat. Add ½ cup water the thin it. Reduce to low and cook 5 minutes. Add shredded turkey, cover, and set aside.
Prepare Masa - Make masa by combining masa harina and chicken stock in a bowl with a wooden spoon. In the bowl of an electric mixer, beat lard at medium speed to aerate, 1-2 minutes. Beat in masa a handful at a time, scraping down the sides occasionally. If masa hasn't reached the consistency of a very thick, pasty porridge, a few tbsp water or chicken stock to get there. Once there, beat in remaining salt.
Assemble and Steam Tamales - Briefly run each banana leaf rectangle over an open flame or hot griddle to make them pliable. Stack them on a worksurface. Place a heaping ½ cup of masa on each. Flatten into a slightly oval shape. Spoon about ¼ cup of the turkey-mole mixture over the masa. Place 2 shorter strings under the leaf and fold top over masa, fold in sides and fold bottom up over first folds. secure by tying each string tightly and then tie from side to side with the longer string to create a sealed packet. Repeat with the rest.
Steam Tamales - Place a roasting pan with a wire rack over the stove. Pour boiling water to just below the rack. Turn heat to medium-high, place packets on rack and cover with a few banana leaves to help absorb the steam. Seal everything with aluminum foil and steam for 45 to 60 minutes. Keep a kettle of hot water nearby in case more steaming water is needed.Serve Tamales - When they are done, remove the foil and banana leaves topping the tamales. Allow them to cool, unopened, for 10 minutes. Each guest unwraps their own.