Cut off the ends of the bunch of buk choy to separate the leaves. Gently wash the leaves in a sink of cold water to remove any dirt and grit. Drain.
Put the leaves in a large heatproof bowl. Pour boiling water over the top and leave to blanch for 3–4 minutes. The leaves should be bright green, and the stems should retain their crunchiness. Drain well, then transfer to a heatproof serving plate.
Meanwhile, heat the oil in a small saucepan over a moderate heat for about 1 minute, or until it begins to smoke. Gently pour the hot oil over the choy, being careful as the oil may splatter. Drizzle with the oyster and soy sauce. Serve while hot.
• You can cook any other Asian greens in the same way. • Another way to prepare the buk choy is to cook it in a saucepan of boiling water for 1–2 minutes.