Heat the oil in a medium saute pan over high heat until almost smoking. Add the onion and cook until soft, 2 to 3 minutes. Add the garlic and cook for 30 seconds. Add the ancho powder, paprika, cumin and cayenne and cook for 1 minute. Add 1/2 cup of water and cook until the mixture becomes thickened and the water reduces. Let cool slightly.
Place the butter in a food processor, add the spice mixture and Worcestershire sauce and process until smooth. Season with salt and pepper, scrape the mixture into a small bowl, cover and refrigerate for at least 30 minutes to allow the flavors to meld. Bring to room temperature before serving and spread the butter over the corn while hot.
Heat the grill to medium.
Pull the outer husks down the ear to the base. Strip away the silk from each ear of corn by hand. Fold husks back into place and tie the ends together with kitchen string. Place the ears of corn in a large bowl of cold water with 1 tablespoon of salt for 10 minutes.
Remove corn from water and shake off excess. Place the corn on the grill, close the cover and grill for 15 to 20 minutes, turning every 5 minutes, or until kernels are tender when pierced with a paring knife. Remove the husks and eat on the cob or remove the kernels.
How to remove corn kernels from cob: To remove kernels from cobs of either raw or cooked corn, stand cob upright on its stem end in a large pan, holding tip with fingers. Cut down the sides of cob with sharp paring knife, releasing kernels without cutting into cob. Run dull edge of knife down the cob to release any remaining corn and liquid.