Cambodian Black Pepper Beef (Lok Lak)

Ingredients

1/3 cup oyster sauce
1/4 cup crushed garlic (about 8 garlic cloves)
3 tablespoons cooking rice wine
2 3/4 tablespoons raw sugar
2 tablespoons soy seasoning sauce (such as Golden Mountain) 2 tablespoons dark soy sauce
2 1/2 teaspoons crushed plus 1 teaspoon coarsely ground Kampot or other black peppercorns, divided
2 tablespoons cornstarch
2 tablespoons water
2 pounds flank steak, cut into 3/4-inch cubes
2 tablespoons olive oil
2 cups thinly sliced red onion (from 1 medium onion)
2 tablespoons fresh lime juice (from 1 lime)
1 teaspoon coarse sea salt
8 butter lettuce leaves
1 unripe red tomato, cut into 8 wedges

Instructions

Stir together oyster sauce, garlic, rice wine, sugar, soy seasoning sauce, dark soy sauce, and crushed Kampot peppercorns in a small bowl.
Stir together cornstarch and 2 tablespoons water in a medium bowl until cornstarch is dissolved; add beef, and toss to coat. Add 1/4 cup of the oyster sauce mixture; cover and refrigerate 8 hours or overnight. Cover remaining oyster sauce mixture, and set aside.
Heat oil in a wok over high. Carefully add beef mixture to wok, and cook, shaking wok often, until beef has a brown sear, 4 to 5 minutes. Add red onion and remaining oyster sauce mixture, and cook, shaking wok often, 2 more minutes.
Stir together lime juice, sea salt, and coarsely ground Kampot peppercorns. Place beef, lettuce leaves, and tomatoes on a platter, and serve with lime sauce.