
Step 1 · Prepare the OK Sauce
Place all the sauce ingredients except the cornflour mixture in a wok and heat gently, stirring until the sauce starts to boil. Lower the heat and simmer for a few minutes. Pour in the cornflour mixture, stirring until thickened. Remove from the heat and set aside.
Step 2 · Heat Oil for Frying
Heat enough oil to deep-fry the beef in a large saucepan or wok to 180°C (350°F).
Step 3 · Coat the Beef
In a large bowl, massage the beaten egg into the beef slices. Tip the cornflour onto a large plate and coat the beef strips a few at a time, making sure each piece is covered and shaking off any excess.
Step 4 · Deep-Fry the Beef
Carefully lower the coated beef into the hot oil in batches and deep-fry for 2 to 3 minutes, or until golden brown and crisp. Transfer to a wire rack or a plate lined with kitchen paper to drain.
Step 5 · Combine and Serve
Heat the remaining 1/2 tablespoon oil in a non-stick wok and fry the onion until tender. Add the fried beef and sauce. Mix thoroughly to coat each piece, then transfer to a serving plate and serve.