Chop up leeks, potatoes, celery. It's all going to be blended, so precision isn't super important, but you want things to cook evenly.
Soften leeks in butter.
Add other veggies and stock. Simmer until everything is soft. About 30 minutes
Blend soup until smooth. Add cream, sour cream, worcester sauce, nutmeg, sherry, salt, and pepper to taste.
Garnish with chopped chives and serve.