COVER THE BLACK BEANS with warm water for 5 minutes. Drain. Rinse thoroughly to remove salt. Put into a bowl with the garlic and ginger; mash into a paste and set aside. Slice the beef against the grain into 1/4-inch thick slices; toss with the beef marinade. Set aside for 10 minutes. Preheat a wok until hot. Add 2 tablespoons of the oil. Over high heat, add beef and stir-fry for a minute or until seared; remove and set aside. While wok is hot, add remaining oil, salt and reserved black-bean paste; stir-fry until fragrant, a few seconds. Toss in the onions, stir-fry for 10 seconds, then add the asparagus in 2-or-3 batches, seconds apart, making certain the wok is hot before adding the next batch. Toss and stir until asparagus are coated with the oil. Sprinkle with soy sauce, toss together, then pour in the stock and bring to a boil. If the asparagus needs more cooking, cover for a minute. Meanwhile, stir the cornstarch, water, sugar and oyster sauce into a smooth paste. When the asparagus is tender but still crisp, add the cornstarch liquid into the center of the wok. Immediately stir until thickened, about 10 seconds. Return the beef, add a desh of sesame oil; toss to mix. Serve hot over rice.