- Melt butter in large stockpot. Simmer clean chopped leeks until soft, about 20 minutes, stirring often.
- Add chicken stock, and sliced aspargus. Bring to boil.
- Reduce heat and simmer 30 minutes or until asparagus is very soft.
- Puree stock in blender, a batch at a time. Return to pot and add tips, simmering until tender but still firm, about 5 minutes. Season to taste with salt and pepper.
- Ladle in bowl and top with dollap of sour cream and chopped chives.
(In the spring, the soup looks lovely toppped with chive blossoms. When the weather is warm, serve the soup cold blended with 1/2 cup of heavy cream.)