1 leek - cut into about 2 cm long slices on the diagonal
5g corn starch - dissolved in 10g water
1. Dredge beef pieces in corn starch, taking care to coat all sides and shake off any excess.
2. Heat up 3 to 5 tbsp oil in a wok or a skillet over medium heat and add the beef. Cook it in small batches for about 2 minutes (no need to cook completely as it will cook again with the sauce). Transfer the beef to a plate to drain the excess oil. Set aside.
3. In a wok, add 1 tbsp vegetable oil and fry ginger and garlic until fragrant over medium-high heat. Add leek and fry until wilted, then return the beef into this wok, stir-fry all together.
4. Add the 'ingredient A', stir continuously. Bring it to boil. Stir-fry all together until the beef is well coated with sauce and cooked through. Finally add diluted corn starch to thicken the sauce.