Preheat the broiler. Place the tomatoes and jalapeños on a small baking sheet lined with aluminum foil. Place under the broiler and roast anywhere from 10 to 15 minutes, flipping a couple times in between, until the tomatoes’ and chiles’ skin is completely charred, they are mushy and soft, and the juices have started to come out of the tomatoes.
Alternatively, you can char the tomatoes and jalapeños on a preheated comal, set over medium heat, for the same amount of time, flipping as they char.
Place the charred tomatoes and jalapeños in a molcajete along with the salt and mash to your desired chunkiness. Or you can put everything in the blender and pulse a couple times. Serve.