stir-fried lemongrass beef with asian greens

Thanks to epicurious
Ingredients

1 1/2 pounds beef top sirloin, fat trimmed, cut lengthwise in half
3 tablespoons minced lemongrass
4 tablespoons fish sauce (nam pla)*
1 1/2 tablespoons soy sauce
1 1/2 teaspoons sugar
3 garlic cloves, minced
4 tablespoons peanut oil
3 tablespoons fresh lime juice
1 large shallot, minced
1 tablespoon minced seeded serrano chile (Thai chili stead)

1 head of bok choy, torn into 1-inch pieces
2 cups thinly sliced red onions
1 cup (packed) opal basil** or regular basil leaves (didn't have)

Preparation

Freeze beef 30 minutes. Using large knife, thinly slice beef crosswise. Mix meat, lemongrass, 3 tablespoons fish sauce, soy sauce, 3/4 teaspoon sugar, and garlic in large bowl. Sprinkle generously with black pepper.

Whisk 3 tablespoons oil, lime juice, shallot, chili, 1 tablespoon fish sauce, and 3/4 teaspoon sugar in bowl to blend. Season dressing with salt and pepper.

Place mustard greens, bok choy, onions, and basil in large bowl. Add 3/4 of dressing; toss to coat. Season salad with salt and pepper.

Heat 1 tablespoon oil in heavy large skillet over high heat. Working in 2 batches, stir-fry meat until cooked to desired doneness, about 35 seconds for rare. Add to greens. Add remaining dressing and toss to combine. Serve immediately.