The key to the rewarding, full-flavor of Mexican sauces and other dishes is in the preparation of the ingredients. And this preparation is time-consuming. Garlic, onions, tomatoes, and tomatillos are roasted on a dry griddle before being peeled and cooked.
Chiles also require various prefatory stages before they are ready to be used.
The seeds and veins of some chiles have to be carefully removed before they are tolerable. Sometimes the chile seeds themselves are roasted on their own.