Rub the meat all over with a few tablespoons of oil. Pierce at close intervals with the tip of a small, sharp knife. Rub thoroughly on all sides with the salt and pepper, rubbing them well into the incisions.
To prepare the marinade, place the ancho chiles in a bowl, cover with boiling water, and let soak until softened, about 10 minutes. Drain the chiles. Working in batches if necessar