In a skillet, char tomatoes and tomatillos on all sides.
Halfway through the charring of the tomatoes and tomatillos, add onion and garlic to the skillet.
Cook for 2 minutes.
Let everything cook for 1-2 minutes more, or until onion is translucent.
With your spatula, move the tomatoes and tomatillos on their sides, making sure they char on all sides.
Remove everything from the skillet and set aside until ready to use.
In a clean skillet, add oil and dried chile de arbol. If you like it spicier, add more chile.
Cook for 1 minute, stirring constantly. Do not let the chiles burn, or the salsa will be bitter.
Place all the chile de arbol and as much of the oil from the skillet in a blender.
Add the tomatoes, tomatillos, onion, garlic, salt, and water to the blender.
Blend until smooth.
Pour into a salsa bowl. Enjoy!