Grilled Flank Steak with Prune-and-Pasilla Adobo

• MAKE-AHEAD

Ingredients

1. 3 dried pasilla chiles (see Note)
2. 1/4 cup pitted prunes
3. 2 tablespoons vegetable oil
4. 1 small onion, finely diced
5. 2 garlic cloves, minced
6. 2 tablespoons sugar
7. 1/4 teaspoon ground cinnamon
8. 1 tablespoon sherry vinegar
9. 1 tablespoon mezcal (see Note)
10. 1/4 cup chicken stock
11. Salt and freshly ground pepper
12. One 1 3/4-pound flank steak

1. In a shallow, heatproof bowl, cover the pasillas with 1 cup boiling water; carefully top with a small plate to keep the pasillas submerged. Let the chiles stand until softened, about 20 minutes. Meanwhile, in a small saucepan, cover the prunes with water and bring to a boil. Cover and let stand until softened, about 10 minutes.
2. Drain the prunes and transfer to a blender. Transfer the pasillas to a work surface; reserve 1/2 cup of the soaking liquid. Discard the pasilla stems and seeds and coarsely chop the chiles. Add the pasillas and their reserved soaking liquid to the blender and puree.
3. Light a grill or preheat a grill pan. In a medium saucepan, heat the vegetable oil. Add the onion and garlic and cook over moderately low heat until softened, about 7 minutes. Add the pasilla chile-prune puree along with the sugar, cinnamon and sherry vinegar and bring to a simmer over moderately high heat. Stir in the mezcal and stock and simmer for 1 minute. Season the adobo sauce with salt and pepper.
4. Season the flank steak with salt and pepper and coat it with 1/4 cup of the adobo sauce. Grill the steak over moderately high heat, turning once, until medium-rare, about 5 minutes per side. Transfer the steak to a carving board and let rest for 5 minutes. Thinly slice the steak across the grain and serve with the remaining pasilla-prune adobo sauce.