Put the flour, salt, and butter in the food processor fitted with the plastic blade, and process until lumpy. Slowly add the water and process until the dough forms a ball on the blade. Add a bit more water if needed. Refrigerate the dough for at least 1/2 an hour until well chilled. Preheat the oven to 450° F. Roll into a circle 2 inches larger than your quiche dish. Press into quiche dish and crimp the edges. Prick the crust with a fork, and bake blind for 8 minutes (lined with foil and weighted with beans or pie weights). Remove the foil and weights and prick the crust again. Return to bake for another 4 minutes.
Sauté the leeks in the butter until golden; season with salt and pepper. Grate the cheeses in the food processor, tossing with the flour. Add the eggs, milk, and a bit of salt and pepper. Mix well.
Spread the leeks across the bottom of the crust. Pour the custard over the leeks, and arrange the tomatoes on top of the pie. Bake for 5 minutes at 400° F. and then 30 minutes at 325° F. or until a knife inserted at the center comes out clean. Serve warm or at room temperature.