First, lay the flank steak flat on a cutting board. Cut off all the fat and silver skin. Silver skin doesn’t break down when cooking and will make the meat tough. Then, slice the steak lengthwise into two equal pieces.
Hold your knife at a 45-degree angle and cut against the grain into pieces about 1 ½ to 2 inches long, aiming for half an inch thick.
Place the sliced beef in a glass or non-reactive bowl. Add soy sauce, white grape juice, rice vinegar, sesame oil, black pepper, and cornstarch. Mix everything by hand to coat each slice evenly.
Cover the bowl tightly with plastic wrap and refrigerate for at least two hours, or overnight for more flavor.
Prep the Vegetables: While the beef marinates, cut the sweet onion into 1-inch chunks. Clean and seed both bell peppers, then cut them into 1-inch chunks to match the onion. Mince the garlic and grate the ginger. Set these aside near the stove.
Mix the Pepper Garlic Sauce: In a medium bowl, whisk together soy sauce, black vinegar, oyster sauce, chili crisp oil, spicy bean paste, and brown sugar until smooth. Set this sauce aside near the stove.
Heat 2 tablespoons of peanut oil in a wok or large pan over high heat until the oil shimmers. Add the beef in small batches, giving each piece space to touch the hot surface. Sear each batch for about 2 minutes.
Then, remove the beef to a wire rack or plate to drain. Repeat until all the beef is seared.
Add the last tablespoon of peanut oil to the pan. Once it shimmers, add the sesame seeds and stir for about 30 seconds until fragrant. Next, add the ginger, garlic, onion, and both peppers.
Stir-fry for 1 ½ to 2 minutes until the peppers are bright and the onion is soft but not fully cooked.
Add the seared beef back to the pan. Pour in the pepper garlic sauce and stir everything together. Cook for one more minute until the sauce thickens and coats each piece.
Spoon the pepper steak over steamed rice or serve it over shredded cabbage for a lighter, low-carb option. This recipe serves about four people as a main dish.
