Toast Sichuan peppercorns in a dry skillet until fragrant; grind into a fine powder.

Steep tofu cubes in boiling water for 5 minutes; drain and set aside.

Whisk together hot bean paste, black-bean paste, 2 tablespoons oyster sauce, and chili powder.

Whisk together cornstarch and 3 tablespoons water.

Heat peanut oil in a wok or large saute pan.

Stir-fry beef, ginger, garlic, and scallions until meat is browned.

Add rice wine and cook until moisture evaporates.

Add hot bean paste mixture and cook until oil turns red.

Add tofu, leeks, stock, light and dark soy sauces, and remaining 2 tablespoons oyster sauce; bring to a boil.

Recombine cornstarch mixture, then add to pan and cook until juices thicken slightly.

Transfer to a serving dish; sprinkle with Sichuan peppercorn powder and cilantro if using. Serve immediately.