Source: Julia's Kitchen
3 Tbs butter
3 cups sliced or minced leeks
3 Tbs flour
2 qts hot water (or 4-5 cups plus milk added at end)
1 Tbs salt; pepper to taste
4 cups potatoes (1½ lb), chopped
⅓-½ cup cream or sour cream, or 2-3 Tbs butter
2-3 Tbs minced parsley or chives