Arbol chiles are commonly found whole, dried with stems, whole dried without stems and ground. As with any chile you'll get the best flavor by toasting whole chiles then grinding them. That being said the flavor from the commercially ground product is quite good and is a real time saver.
Make sure to purchase pure chile powder with no preservatives or additives.
This hot salsa is great over tacos. Recipe by La Cienaga, Chicago, IL
Place tomatoes in a small saucepan with enough water to cover and bring to a boil.
Heat 1 tablespoon of oil in a heavy skillet and stir-fry chlies for 1-2 minutes to bring out the flavor. Don't allow the chiles to burn. Remove chiles with a slotted spoon and place on paper toweling to drain.
Add the remaining oil to the pan and add the guajillo chiles and garlic and stir-fry for 3- minutes. The garlic should be lightly browned but not too dark or it will be bitter. Remove chiles and garlic with a slotted spoon and place on paper toweling to drain.
Place tomatillos in the pan, swirling them around to fry until the skin is blistered and the tomatillos are cooked through. Remove from pan and place in a small bowl and allow to cool.
Remove cooked tomatoes and place in a bowl and allow to cool. Reserve the cooking liquid.
Place all the ingredients including tomatoes, tomatillos, chiles, and spices in a blender jar along with 2-3 cups of the tomato cooking liquid and blend until smooth.