Place the leeks, potatoes and butter in a large bowl. Cover and cook on HIGH MICROWAVE for 5mins.
Gradually add the stock and seasoning.
Re-cover and cook on HIGH MICROWAVE for 15mins or until the vegetables are tender. Stirring halfway.
Allow to cool slightly.
Blend with hand blender until smooth.
Stir in the crème fraiche and season to taste. Heat on MEDIUM MICROWAVE for 3 mins or until piping hot.