1. Heat oven to 350F. Coat 13x9 inch baking dish with vegetable cooking spray.
2. Discard green portions from leeks. Slice white portions of each lengthwise in half; cut crosswise into slices. rinse leeks well to remove all sand; drain.
3. Heat water and spread in Dutch oven or nonstick skilled over high heat. Add leeks, sliced onions, and 1/2 teaspoon salt; toss to coat well. Reduce heat to low; cover and simmer, stirring until leeks and onions are tender, 10 minutes.
4. Stir in ham, 3/4 teaspoon salt, the pepper, and thyme. Cook uncovered, stirring over medium-high heat until liguid is evaporated and leeks and onions are golden.
5. Meanwhile, slice potatoes thin.
6. Place flour in large bowl; gradually whisk in milk until smooth. Gradually stir into leek-onion mixture. Bring to boil over high heat, stirring until thickened; boil 1 minute.
7. Spoon 1/2 cup milk mixture into bottom of prepared pan. Top with half the sliced potatoes. Spoon half of remaining sauce over potatoes. Arrange remaining potatoes; cover with remaining sauce.
8. Cover dish with foil and bake 1 1/4 hours. Sprinkle parsley and bake uncovered 15 minutes more, until potatoes are tender.
Recipe By : Ladies' Home Journal - Jan. 1995