Step 1: Marinate the Pork : In a bowl, combine pork cubes, soy sauce, Shaoxing wine, salt, white pepper, and egg. Mix well, cover, and let marinate for 15–20 minutes at room temperature.
Step 2: Coat and Fry the Pork : Heat vegetable oil in a wok or deep pan to 350°F (175°C). Coat each marinated pork piece in cornstarch, shaking off excess. Deep-fry in batches for 3–4 minutes, until golden brown and crispy. Remove with a slotted spoon and drain on paper towels. For extra crispiness, double-fry the pork: once more for 1–2 minutes after the first fry.
Step 3: Make the Sauce : In a small bowl, whisk together ketchup, vinegar, brown sugar, soy sauce, pineapple juice, and water. In a saucepan or wok, heat the mixture over medium heat until it begins to bubble. Add the cornstarch slurry and stir continuously until the sauce thickens and turns glossy.
Step 4: Stir-Fry the Vegetables : In a wok or large skillet, heat 1 tbsp vegetable oil over medium-high heat. Add garlic, onions, and bell peppers, and stir-fry for 2–3 minutes until just tender but still crisp. Add pineapple chunks and toss for another minute.
Step 5: Combine Everything : Add the fried pork to the wok with the vegetables. Pour the sweet and sour sauce over the top. Toss everything together until the pork and veggies are evenly coated in sauce.
Step 6: Serve Hot : Serve immediately over steamed jasmine rice or fried rice, and garnish with chopped scallions or sesame seeds if desired.