Heat a large cast-iron skillet over high heat. Add the tomatoes, garlic, chiles and onion and cook, turning occasionally, until charred on all sides, about 3 minutes for the garlic, 4 to 5 minutes for the chiles, 6 to 8 minutes for the onion and 8 to 10 minutes for the tomatoes. Transfer to a plate to cool. When cool enough to handle, peel the garlic.
Add the tomatoes, garlic, chiles, onion, cilantro, lime juice and 1 tablespoon salt to a blender and puree on low speed, stopping to scrape the sides and bottom to ensure an even texture, until the salsa is almost smooth but some small pieces remain. Season with salt and more lime juice if needed.
When blending hot liquid, first let it cool for five minutes or so, then transfer it to a blender, filling only halfway. Put the lid on, leaving one corner open. Cover the lid with a kitchen towel to catch splatters, and pulse until smooth.