Cut green tops from leeks, and discard. Chop white portions.
Melt butter in a Dutch oven; add leeks and celery, and sauté until tender. Add flour, and cook, stirring constantly, 3 minutes. Stir in broth, 3 cups water, and salt; bring to a boil. Reduce heat, and simmer, stirring occasionally, 15 minutes.
Microwave cream cheese and yogurt in a 2-quart microwave-safe bowl at HIGH for 15 to 20 seconds or until warm; whisk until smooth. Whisk in egg yolks; gradually whisk in 2 cups leek mixture. Stir cream cheese mixture and pepper into leek mixture. Cook over low heat, stirring occasionally, until thoroughly heated. (Do not boil.) Sprinkle with chives, if desired.
This was ok. It had a good flavor but I expected it to be thicker. Not bad but probably won't make it again.