Boil potato cubes in boiling water for 5 minutes until half-cooked (Tip: Add a little salt while boiling, then drain and set aside).
Heat pan with a little oil over medium-high heat. Pan-fry beef tenderloin cubes until 70% cooked, then remove and set aside.
Add the pre-cooked potato cubes and stir-fry until they turn slightly golden with crispy edges (about 3–4 minutes. Tip: Do not use too high heat to prevent sticking). Then add tri-color bell pepper chunks and stir-fry until fragrant.
Return the beef cubes to the pan, add 1/2 pack of Sauce for Black Pepper Chicken. Reduce to medium heat and stir-fry all ingredients until the sauce thickens and evenly coats the potatoes and beef (adjust sauce amount to taste).