Asian broad bean chili paste (or sauce) is also known as doubanjiang or toban djan; our favorite, Pixian, is available online. Lee Kum Kee Chili Bean Sauce is a good supermarket option. If you can’t find Sichuan chili powder, an equal amount of Korean red pepper flakes (gochugaru) is a good substitute. In a pinch, use 21/2 teaspoons of ancho chile powder and 1/2 teaspoon of cayenne pepper. If you can’t find fermented black beans, you can use an equal amount of fermented black bean paste or sauce or 2 additional teaspoons of Asian broad bean chili paste. Serve with steamed white rice.
1. Microwave water, 1/2 teaspoon salt, and dried mushrooms in covered large bowl until steaming, about 1 minute. Let sit until softened, about 5 minutes. Drain mushrooms in fine-mesh strainer, reserving liquid; set aside soaked mushrooms and return liquid to large bowl.
2. Place peppercorns in small bowl and microwave until fragrant, 15 to 30 seconds. Let cool completely. Once cool, grind in spice grinder or mortar and pestle (you should have 11/2 teaspoons).
3. Using side of chef’s knife, lightly crush white parts of scallions, then cut scallions into 1-inch pieces. Place tofu and scallions in bowl with reserved mushroom liquid and microwave until steaming, 5 to 7 minutes. Let stand while preparing remaining ingredients.
4. Process garlic, ginger, chili paste, and black beans in food processor until coarse paste forms, 1 to 2 minutes, scraping down sides of bowl as needed. Add 1/4 cup vegetable oil, chili powder, and 1 teaspoon peppercorns and continue to process until smooth paste forms, 1 to 2 minutes longer. Transfer spice paste to bowl.
5. Place reserved soaked mushrooms and fresh shiitake mushrooms in now-empty processor and pulse until finely chopped, 15 to 20 pulses (do not overprocess). Heat 2 tablespoons vegetable oil and mushroom mixture in large saucepan over medium heat, breaking up mushrooms with wooden spoon, until mushrooms begin to brown and stick to bottom of saucepan, 5 to 7 minutes. Transfer mushroom mixture to bowl.
6. Add remaining 2 tablespoons vegetable oil and spice paste to now-empty saucepan and cook, stirring frequently, until paste darkens and oil begins to separate from paste, 2 to 3 minutes. Gently pour tofu with mushroom liquid into saucepan, followed by hoisin, sesame oil, and mushroom mixture. Cook, gently stirring frequently, until dish comes to simmer, 2 to 3 minutes. Whisk soy sauce and cornstarch together in small bowl. Add cornstarch mixture to saucepan and continue to cook, stirring frequently, until thickened, 2 to 3 minutes longer. Transfer to serving dish, sprinkle with remaining peppercorns, and serve. (Mapo tofu can be refrigerated for up to 24 hours.)