3 tbsp. peanut or safflower oil
1 lb. top round steak, thinly sliced across the grain (and cut crosswise if the strips are long)
2 leeks, white and pale-green parts only—cut in half lengthwise, then cut crosswise into 1/2-inch half-moons
Salt and pepper
2-inch piece of fresh ginger, peeled and grated or finely chopped
4 cloves garlic, finely chopped
3 tbsp. hoisin sauce
¼ cup water or beef stock (optional)
1 large head iceberg lettuce—cored, quartered, and cut into 1/2-inch strips
1 tbsp. tamari
1 tsp. toasted sesame oil
Toasted sesame seeds (optional), for garnish
Heat a large skillet or wok over high. Add 2 tbsp. oil, two turns of the pan. When the oil smokes, add the beef and stir-fry until browned, about 2 minutes. Add the leeks; season with salt and pepper. Add the ginger and half the garlic and toss until the leeks soften, about 2 minutes more. Add the hoisin and the water if the beef and leeks seem dry. Transfer to a bowl.
Add the remaining 1 tbsp. oil, one turn of the pan, to the wok. When the oil smokes, add the lettuce and stir-fry just until wilted, about 1 minute. Add the remaining garlic and stir-fry until fragrant, about 1 minute more. Add the tamari and sesame oil; season with pepper. Transfer to a serving dish or dinner plates. Top the lettuce with the beef and leeks. Sprinkle with sesame seeds (if using).