Heat a small cast-iron skillet. Add the garlic and chiles and cook over moderate heat, turning, until lightly charred all over, about 15 minutes. Let cool, then peel the garlic. Split the chiles lengthwise and remove most of the seeds. Coarsely chop the chiles. Transfer the garlic and chiles to a food processor or blender. Add the parsley, cilantro and the 1/2 cup of olive oil and puree. Season the pesto with salt and transfer to a clean jar. Pour in enough olive oil to cover the pesto by 1/4 inch and refrigerate for up to 2 months.