Method

1. Melt ½ the butter in a large saucepan over a medium heat. Add leek and cook for 5 minutes or until softened. Remove ½ the leek and set aside. Add celery, garlic, thyme and bay leaves to pan and cook for a further 5 minutes.

2. Sprinkle flour over mixture in pan and cook, stirring, for 2 minutes or until mixture begins to stick to bottom of pan. Add stock and bring to a simmer.

3. Meanwhile, cut ²/³ of the potatoes into 1cm cubes and set aside. Chop remaining potatoes and add to pan. Cook for 30 minutes or until potato is tender. Season soup with salt and pepper, then pour into a blender and pulse until smooth.

4. Steam reserved potato over a saucepan of simmering water for 8-10 minutes or until tender, then fold into soup. Serve with chives, sour cream and toast.