Soak the corn in a large container of water for 1 hour. Prepare the grill. Put the soaked cobs on the hot grill and cook for 30 to 40 minutes, turning frequently. The corn is done when it feels soft when you press on it.
While the corn is grilling make the lime butter: In a small bowl add the butter, lime zest, chervil, and salt and pepper, to taste. Mix well and spread onto a large plate. Spread the queso fresco onto another plate.
Take the corn off the grill and carefully peel back the husks (it will be hot). Remove the corn silk and tie the husks in a knot so you can hold on to it like a handle. Roll in the lime butter and then roll in the queso fresco; sprinkle with the Ancho Chile Rub. Place on a large platter and serve immediately.
For the Ancho Chile Rub:
For the spice rub: Toast the ancho chile pieces over low heat in a dry skillet until fragrant, shaking the pan so they don't scorch. Put the chiles in spice grinder and pulse to a powder. Add the remaining ingredients and buzz again to combine.