Step 1

Thinly slice the beef across the grain into strips, each about 3 inches long, 1 inch wide, and a scant ¼ inch thick. Transfer to a bowl. Add the sugar, soy sauce, fish sauce, and cornstarch. Mix well and set aside to marinate the beef for 15 minutes.

Step 2

Meanwhile, trim the asparagus of its woody ends, then cut on a steep diagonal into pieces about 2 inches long.

Step 3

Warm a large skillet or wok over high heat. Swirl in 1 tablespoon oil, then add the asparagus. Quickly stir and toss for about 30 seconds to heat through, until glossy and a brighter shade of green. Sprinkle in the salt and pour in the water. Lower the heat slightly, then cover. Let steam-cook for 1 to 2 minutes, until the asparagus have slightly softened. Transfer to a plate.

Step 4

Replace the pan to warm it over high heat. Swirl in the remaining 1 1/2 tablespoons oil, then add the onion, garlic, chile, and lemongrass. Stir-fry for 1 minute, until fragrant.

Step 5

Add the beef, spreading it out to one layer. Let it sear for a minute, then stir-fry it for another 2 minutes, or until just cooked through. Return the asparagus to the pan. Cook for another 15 seconds until the asparagus has heated through and finished cooking. Turn off the heat, let rest for about 30 seconds, taste and season with a sprinkling of extra salt, if needed. Transfer to a plate and serve.