Method

1. Preheat the oven to 200°C. Grease a 1.5 litre capacity baking dish with butter
2. Melt the butter in a small frying pan and gently cook the leek for 15 mintues until tender.
3. Whisk the egg white in a clean bowl until stiff but not dry. In a separate bowl lightly mix the egg yolk.
4. Whisk the egg white in a clean bowl until stiff but not dry. In a separate bowl lightly mix the egg yolk.
5. Pour the mixture into the baking dish and cook for 10 minutes until puffed, golden and set.
6. Serve immediately.