Traditionally, Spanish romesco sauce is made with roasted red bell peppers and almonds. Hatch chiles give this Catalonian sauce a zippy Southwestern spin, and you could sub tomatillos for the tomatoes. Hatch chiles are unique in that they come in mild, medium, hot and extra-hot varieties. I used medium Hatch chiles, which lend the sauce pleasant heat. Serve it with grilled fish or chicken, use it as a dipper with chunks of rustic bread, or toss it with hot pasta.
Move the oven rack to the top position and preheat the broiler.
Arrange the chiles, tomatoes and onion in a single layer on a baking sheet lined with foil. Broil 15 minutes or until blackened, turning halfway through cooking time.
Transfer the chiles and tomatoes to a large bowl, cover with a plate, and let stand 15 minutes or until cool enough to handle. Peel and seed the chiles and tomatoes.
Combine the chiles, tomatoes, onion, and garlic in a food processor and process until chopped. Add the bread and nuts and process until chopped. Add the oil, vinegar, and salt and process until smooth. Transfer to a clean jar and refrigerate for up to 5 days or freeze for up to 2 months. (Makes about 2 cups.)