How to Make It
Preheat a large cast-iron skillet or griddle. Add the pasillas and toast over high heat, pressing them down with a spatula and turning once, until pliable and fragrant, about 1 minute. Transfer the pasillas to a heatproof bowl and cover with 2 cups of hot water. Let stand for about 30 minutes, until the pasillas are completely rehydrated.
Meanwhile, in the same skillet, roast the tomatoes and garlic over high heat until charred, about 12 minutes.
Transfer the rehydrated pasillas to a blender and add 1 cup of their soaking liquid. Puree until smooth, then strain through a coarse sieve into a bowl.
In a large skillet, heat 1 tablespoon of the oil. Add the pasilla puree and cook over moderate heat, stirring occasionally, until deep red and reduced nearly to a paste, about 15 minutes.
Peel the roasted garlic and add it to the blender along with the tomatoes. Puree until smooth, then strain through a coarse sieve into the skillet with the pasilla paste; bring to a boil. Simmer the salsa over moderately low heat for 15 minutes, stirring occasionally. Season with salt and pepper and keep warm.
In another large skillet, heat the remaining 3 tablespoons of oil until shimmering. Add the mushrooms, season with salt and pepper and cook, stirring occasionally, until the mushrooms are browned, 3 to 5 minutes. Stir in the pasilla salsa and bring to a simmer. Add the crushed tortilla chips and cook, tossing, for 3 minutes. Transfer the chilaquiles to a platter or plates and garnish with queso fresco, crema and chopped onion and cilantro. Serve right away.
Pasillas are long, black dried chiles with a fruity, herbaceous flavor. They are available at Latin markets.