How to Make It
In a large skillet, bring the water to a boil. Add the leeks, wine, bay leaf and a large pinch of salt and simmer over moderate heat until the leeks are tender, about 25 minutes. Using a slotted spoon, transfer the leeks to a plate, keeping them intact. Add the cream and shallot to the cooking liquid and simmer over moderate heat until reduced to 1 1/4 cups, about 6 minutes. Add the lemon juice and season with salt and pepper.
Preheat the oven to 500°. Arrange the leeks, cut side up, and the ham in a large gratin dish. Pour the cream sauce evenly over the leeks and ham. In a small bowl, combine the pistachios and melted butter and scatter over the leeks. Bake in the upper third of the oven for about 8 minutes, or until golden brown on top. Serve piping hot.