How to Make It
In a medium skillet, toast the chiles over moderate heat, turning occasionally, until pliable and blistered in spots, about
1 minute. Add the tomatillos, onion, garlic, brown sugar and chicken broth and bring to a boil. Cover partially and simmer over moderately low heat, stirring occasionally, until the vegetables are very soft, about 20 minutes.
Transfer the mixture to a blender and let cool slightly, then puree until smooth. Strain the sauce through a fine sieve and season with salt. Serve warm.