Wrap the head of garlic with aluminum foil and roast for 40 minutes. Set aside until cool enough to handle.
Squeeze the cloves of garlic from their papery skins into a small glass bowl. Add the butter and ancho powder, mixing well to combine. Season with salt and pepper. Place a piece of plastic wrap on a work surface, spoon the butter into the middle and roll into a cylinder. Refrigerate until set, at least 30 minutes. (The butter can be made ahead and will keep for up to a week.)
Preheat a grill or grill pan to high heat.
Grill the corn, turning occasionally, until browned in spots and the kernels are tender, 15 to 20 minutes. Brush with the ancho chile butter and serve.