Heat a heavy medium frying pan over medium-high heat until hot. Cook tomatoes and jalapeños until blistered and charred on all sides, turning as needed, 9 to 10 minutes. Add chiles de árbol and cook, turning, just until fragrant, about 15 seconds.
Transfer tomatoes to a blender. Let chiles cool, then discard stems and peel off a little of the blackened skins. Add chiles to blender with garlic, onion, 2 tsp. salt, and 6 tbsp. water. Whirl until fairly smooth. Add cilantro and whirl just to blend. Season with more salt to taste.
*Find at Latino markets and well-stocked grocery stores.
Make ahead: Up to 1 day, chilled.