Line a baking sheet with aluminum foil. Lay 6 of the pepper halves, cut side down, on the foil, and broil 2 inches from the heat until well charred, 5 to 10 minutes. Transfer the peppers to a plastic bag and seal the bag. Allow the peppers to steam in the bag for 10 minutes. Then remove them from the bag, and slip off and discard the skins.