Brush a large skillet with oil. Add the garlic and jalapeños to each. Don't worry if you can't fit all the peppers in the skillet at the same time, you can transfer some out to cool. Cover and cook over low heat, turning the jalapeños occasionally, until they are blistered all over and the garlic is softened, about 15 minutes. Transfer to a plate to cool. Peel the jalapeños and discard the stems, seeds and cores. Peel the garlic cloves.
Transfer the jalapeños and garlic to a blender and add the olive oil, lime juice and cilantro. Blend until smooth. Scrape the sauce into a bowl, season with salt. Transfer the sauce to jars and refrigerate. Can be stored up to 2 months.