How to Make It
In a bowl, mix the sherry with 2 teaspoons of the soy sauce and the cornstarch. Add the lamb and stir to coat.
In a bowl, combine the hoisin sauce, vinegar, chile-garlic paste, sugar and the remaining tablespoon of soy sauce.
In a wok, heat 2 tablespoons of oil over high heat until smoking. Add the garlic; stir-fry until fragrant, 15 seconds. Add the lamb; cook, stirring, until lightly browned, 3 minutes; transfer to a plate.
Add the remaining 1/2 tablespoon of oil to the wok. Add the beans and stir-fry until crisp-tender, about 4 minutes. Add the onion and cook until softened, 2 minutes. Add the pepper and leek and cook, stirring occasionally, until the leek is lightly browned, about 3 minutes. Add the hoisin-vinegar sauce to the wok and cook just until bubbling. Return the lamb to the wok and stir-fry until heated through. Transfer to a platter and serve.