Chorizo and Potato Egg Custard with New Mexican Chile Sauce

Heat a dry heavy skillet (preferably cast-iron) over moderate heat until hot, then toast chiles, pressing down with tongs and turning occasionally, about 1 minute. Transfer to a bowl. Toast garlic in skillet, turning occasionally, until softened and slightly charred, about 5 minutes, then transfer to bowl. Toast cumin in skillet, stirring, until fragrant and a few shades darker, about 30 seconds, then transfer to a blender along with tomatoes and salt. Discard stems and seeds from chiles and add to blender. Peel garlic and add to blender. Purée until smooth.