Add the tomatoes, onions, garlic cloves, Mexican oregano, and 2 cups of vegetable broth to a blender. Add ⅔ of the pasilla chiles and all of the arbol chiles, then mix on high until smooth.
Add the tomatoes, onions, garlic cloves, Mexican oregano, and 2 cups of vegetable broth to a blender. Add ⅔ of the pasilla chiles and all of the arbol chiles, then mix on high until smooth.