Step 1

Preheat the oven to 375°F. In the bowl of a food processor, combine the 1¼ cups flour with the salt. Add the butter and pulse until it is the size of small peas. Lift the lid and add the egg yolk and ice water and pulse until moistened. Turn the dough onto a floured work surface and knead 2 or 3 times, just until smooth. Form the dough into a disc, wrap in plastic wrap, and refrigerate until firm, about 20 minutes. On a floured surface, roll the dough into a 11-inch circle. Gently press the pastry into a 9-inch fluted tart pan with removable bottom and trim the excess. Poke the bottom all over with a fork and chill until firm. Line the pastry with foil and fill with pie weights or dried beans. Bake in the center of the oven for 30 minutes, just until dry. Remove the foil and bake the crust until golden and dry, 15 to 20 minutes longer. Set the tart pan on a sturdy baking sheet.

Step 2

While the pastry bakes, in a large skillet, melt the butter over moderate heat. Add the leeks and thyme, season with salt and white pepper, and cook, stirring occasionally, until softened, but not browned, about 5 minutes. Transfer to a bowl, let cool, then stir in the cheese and salmon. Spread the mixture on the bottom of the pastry. In a bowl, whisk the eggs with the yolk and half & half. Season lightly with salt and white pepper. Pour the custard over the filling and bake in the center of the oven for 30 minutes, until the custard is set, puffed and lightly browned. Transfer the pan to a wire rack to cool for 15 minutes. Remove the ring and cut the quiche into wedges.