Preparation / Directions:
Char poblano chilies over gas flame or in broiler until blackened on all sides. Enclose chilies in paper bag. Let stand 10 minutes to steam. Peel and seed chilies. Toast ancho chilies in heavy large skillet over high heat until color darkens slightly and chilies are fragrant, about 30 seconds per side. Transfer ancho chilies to medium bowl. Add enough hot water to bowl to cover chilies. Let stand until chilies soften, about 20 minutes.
Puree 4 ancho chili halves with 1/2 cup soaking liquid in blender. Add roasted poblano chilies; puree. Season with salt and pepper. Drain remaining 2 chili halves; chill. (Puree and soaked chilies can be made 1 day ahead. Cover separately and chill.)
Preheat oven to 350=F8F. Rinse turkey inside and out. Pat turkey dry. Sprinkle turkey with salt and pepper. Cut remaining 2 ancho chili halves into strips. Place chili strips and onion in turkey cavity.
Mix butter and achiote paste in small bowl to blend. Run fingers between turkey breast skin and meat to loosen. Rub half of achiote butter over turkey breast under skin. Rub butter over outside of turkey. Place turkey in large roasting pan. Tuck wings under turkey. Tie legs together to hold shape. Pour 1 1/2 cups broth into pan.
Roast turkey 45 minutes. Tent turkey loosely with foil. Continue roasting until meat thermometer inserted into thickest part of thigh registers 180=F8F, basting every 30 minutes with pan juices, about 3 1/2 hours. Transfer to platter. Tent with foil.
Pour turkey pan juices into measuring cup. Spoon off fat from pan juices, reserving 1/4 cup fat. Add enough remaining broth to pan juices to measure 3 cups. Return 1/4 cup fat to roasting pan. Place pan over 2 burners set at medium heat. Add Masa Harina; whisk until mixture resembles paste, scraping up any browned bits, about 2 minutes. Gradually whisk in pan juices. Add chili puree; simmer 5 minutes to blend flavors. Season gravy with salt and pepper. Serve turkey with gravy.