If this pie sounds like a cross between baked apples and apple dumplings, well, it is. It's baked with a top pastry only, which molds itself around the apples so handsomely that I don't even bother to invert the pie, lest the pastry vanish beneath the apples. I use Golden Delicious apples here because they hold their shape well. They’re halved, cored, and placed in the pan in a pool of melted butter, brown sugar, and raspberry preserves. A raisin-brown sugar-walnut mixture is spooned into the hollowed cores, à la baked apples, then the pastry is draped over the top, and the pie is baked. Since this bakes up in individual mounds, you don't slice it like a regular pie. Rather, you scoop out the mounds — which look like halved apple dumplings — and serve them with the pan juices. Excellent alone, but even better with chilled Vanilla Custard Sauce.
Put the flour, sugar, and salt in the bowl of a food processor and pulse several times to mix. Remove the lid and scatter the butter pieces over the dry ingredients. Pulse the machine repeatedly — six or seven 1-second bursts — until the butter is broken into very small pieces.
Place the egg yolk in a 1-cup glass measure and add just enough of the water to equal ¼ cup liquid. Using a fork, blend the water and yolk. Remove the lid of the processor and pour the liquid over the entire surface of the dry ingredients. (Don’t, in other words, pour it into one spot.)
Pulse the machine again, in short bursts, until the pastry starts to form large clumps. Don’t overprocess, or the butter will start to melt rather than stay in small pieces.
Tear off a sheet of plastic wrap about 14 inches long and place it nearby. Empty the crumbs into a large mixing bowl. Using your hands, pack the dough as you would a snowball. Knead the dough 2 or 3 times, right in the bowl. Put the dough in the center of the plastic wrap and flatten it into a disk about ¾-inch thick. (The edges will probably crack slightly; just pinch and mold them back into a smooth disk.) Wrap the dough in the plastic and refrigerate until firm enough to roll, about 1 hour.
Combine the raisins, walnuts, ¼ cup firmly packed light brown sugar, and cinnamon in the bowl of a food processor. Pulse repeatedly, until the mixture is finely ground. Set aside.
Select an ovenproof skillet or sauté pan that measures 9 inches across the bottom and 11-12 inches across the top. Melt the butter in the skillet over medium heat, then stir in the remaining brown sugar and preserves. When the mixture is bubbling evenly over the surface of the pan — 30 seconds or so — remove from the heat.
Do not peel the apples; the peels will help them hold together. Do halve them, however, crosswise, and core each half. Place the apple halves in the pan, cut side down. You should be able to get 6 around the outside and 1 in the center. Finely dice the remaining apple half and scatter the pieces between the apples.
Preheat the oven to 400 degrees.
Spoon some of the raisin-walnut mixture into each apple half, compacting it with a finger.
Sprinkle leftover mixture between the apples.
On a sheet of lightly floured waxed paper, roll the pastry into a 12-inch circle with a floured rolling pin. Invert the pastry over the apples, center it, and peel off the paper. Lifting the edge of the pastry, tuck the edge straight down along the inside of the pan. Poke several large vent holes in the pastry with a paring knife, twisting the knife to enlarge the holes.
Lightly brush the pastry with light cream and sprinkle with granulated sugar. Place the pie directly on the center oven rack and bake for 20 minutes. Reduce the oven temperature to 375 degrees and bake until the top crust is golden brown, another 25 minutes.
Transfer the pie to a cooling rack and let cool for at least 20 minutes before serving. Serve with the Vanilla Custard Sauce, if desired.