Preheat a cast iron pan or a
comal over medium-high heat. Optionally, line the pan with aluminum foil. This will save you a bit of cleaning afterwards. Place the tomatoes, garlic, onion and the chile on the pan and roast, frequently turning, until they are nicely browned on all sides and softened up. Garlic and chiles normally get soft and slightly charred first, so remove them as soon as they are done. Then the onion. Tomatoes will need a bit more turning and toasting until they get soft and can be removed.