Cubes of beef tenderloin are supertender in this wonderfully spiced and elegant Vietnamese classic. It’s called “shaking beef” because you shake the pan to toss the beef while cooking it. More Fast Asian Recipes
In a large bowl, combine the garlic, sherry, soy sauce, sugar, pepper and five-spice powder with the 1 tablespoon of oil. Add the beef and turn to coat thoroughly with the marinade. Cover and refrigerate for at least 5 hours or overnight.
In a small bowl, combine the soy sauce with the vegetable oil, sherry, red wine vinegar, minced ginger, sugar, garlic and lemongrass. Let stand for 30 minutes, stirring a few times.
Mound the watercress and red onion on a platter and toss with half of the vinaigrette. Set 2 large skillets over high heat until very hot, about 2 minutes. Add 1 tablespoon of oil to each skillet; when shimmering, add the meat to both skillets in an even layer. Let cook undisturbed, until richly browned on the bottom, about 1 1/2 minutes. Shake the skillet to release the meat and cook for about 30 seconds longer, until medium-rare. Scrape the beef onto the watercress. Drizzle with the remaining vinaigrette, toss lightly and serve right away.
The vinaigrette can be refrigerated overnight. Bring to room temperature before using.