How to Make It
In a large bowl, combine the flour and 1/2 teaspoon salt. Using your fingers or a pastry blender, rub or cut the butter into the flour until it resembles coarse meal. In a measuring cup, combine the egg yolk with the ice water. Stir the yolk mixture into the flour until the dough comes together. Gather the dough into a ball, then divide it in half and pat each half into a 6-inch disk. Wrap each disk in plastic and chill until firm, about 2 hours or overnight.
Preheat the oven to 375°. On a lightly floured surface, roll out one piece of the dough into a 14-inch round. Transfer the dough to a 9-inch fluted tart pan with a removable bottom, fitting it evenly into the pan without stretching. Repeat the process with the remaining dough. Trim the overhanging dough to 1/2 inch and fold it into the tart pan to strengthen the sides.
Line the tart shells with foil and fill with pie weights, rice or beans. Bake in the center of the oven for 20 minutes. Remove the foil and weights and bake for about 10 minutes longer, or until the shells are light golden and fully cooked; if the bottoms bubble, lightly press down with a fork. Transfer the pans to a rack and let the tart shells cool.
In a large skillet, cook the bacon over moderately high heat until brown and crisp, about 8 minutes. Transfer to paper towels to drain, then transfer to a small bowl. Pour off all but 1 tablespoon of the rendered fat from the skillet. Add the leeks to the skillet and cook over moderately high heat, stirring occasionally, until softened but not browned, about 2 minutes. Add to the bacon in the bowl and season with salt and pepper. In a medium bowl, combine the eggs and cream and season with salt and pepper.
Sprinkle 1/2 cup of the Gruyère into each tart shell and top with the bacon-leek mixture. Stir the custard, pour it over the bacon filling in each tart shell and sprinkle with the remaining cheese. Bake for about 30 minutes, or until the custard is set and a knife inserted in the center comes out clean.
Preheat the broiler. Broil each quiche for about 30 seconds to brown the top. Transfer to a wire rack and let rest for 10 minutes before serving.