Preheat the broiler. Lay the tomato and onion halves cut-side down on a foil-lined baking sheet; surround with the tomatillos and jalapeno. Broil until charred, about 5 minutes. Let cool slightly.
Meanwhile, cook the chile de arbol in a small dry skillet over medium-high heat, turning, until toasted, 30 seconds to 1 minute.
Combine the tomatoes, onion, tomatillos, jalapeno, chile de arbol, chipotle and garlic in a blender and puree until mostly smooth. Add the cilantro and puree until incorporated; season with salt. Chill at least 30 minutes before serving.
"This robust, spicy salsa is best made the day before so the rich flavors come together."