Stir and saute leeks and onion in butter for 3 minutes.
Add peeled, sliced potatoes, and chicken stock.
Simmer, covered, for 15 minutes, or until tender.
Put through a food mill or blender.
Add cream, mace, salt and white pepper, and chopped chives.
Alternatively, put half through the blender. Leave the other half chunky.
No real need to add cream. It's quite good without.
Serve hot or cold.