Preparation

• Position a rack in the center of the oven, and heat the oven to 500°F. Line a large rimmed baking sheet with foil.
• Put the tomatoes and serrano on the baking sheet, and roast, turning the chile occasionally, until the chile is browned and softened, about 15 minutes. Remove the chile, and continue to roast the tomatoes until blackened and very soft, 25 to 30 minutes.
• Roughly chop the chile with 1 tsp. salt, and then transfer to a food processor, add the tomatoes and their juices, and pulse until coarsely chopped. Season to taste with salt and serve.