Step 1 To prepare the pak choy, strip the leaves from the stalk and soak in cold water. When there is just the heart of the pak choy left, trim the stalk and leave the heart whole. Drain and cut the pak choy leaves into 4cm lengths. Step 2 Butterfly the prawns by splitting them down their back (but not all the way through). Add the ginger and garlic and stir-fry for about 1 minute, then add the prawns and cook for a further minute.