In a heavy 4 quart pan, melt 1/4 cup butter and onion until wilted. Add cleaned and sliced leeks, potatoes, water and salt. Bring to a boil and simmer, partially covered, for 45 minutes or until potatoes are very tender.
Step 2
Remove from heat and cool if you want. Blend the cooked mixture until smooth. Return to the saucepan; add 1/4 cup butter, cream and chives. Check for seasonings. Heat, but do not boil or the cream will curdle.