For the filling:
Prepare the puff pastry as directed in the recipe and preheat the oven to 400 degrees F (204 degrees C). When the puff pastry is ready to roll, place it on a lightly floured work surface and use a rolling pin to roll it into an 8 by 18-inch rectangle. Place the rectangle on the work surface with the long side facing you. Use a sharp paring knife to cut 2 (1 by 18-inch) strips from the top of the dough. Place the remaining rectangle on a parchment paper-covered baking sheet.
Egg wash: Combine the egg yolks, whole egg, and milk in a small mixing bowl and whip with a hand whisk until well combined. Use a pastry brush to brush a 1-inch border of egg wash along each long side of the rectangle on the baking sheet. Place 1 of the thin strips on each side of the rectangle, over the egg wash. Try to keep the strips straight and even. These edges will keep the filling inside the tart shell, as they rise slightly higher than the rest of the tart. Brush the tops of the 2 strips with egg wash. Use an offset spatula to spread the applesauce down the center of the tart shell.
Filling: Peel, core, and halve the apples. Slice each half into 1/4-inch-thick slices and lay them lengthwise on the tart, overlapping the slices slightly. Use a pastry brush to brush egg wash over the tops of the apple slices. Sometimes I make a decoration along the edge of the dough on the long sides of the tart. To do this, I gently press the tips of my first and second fingers into the dough, right at the edge. Then I use the back of a paring knife to mark the spot between my 2 fingers by pushing the dough in 1/4-inch. I repeat this all along the long sides to give the tart a scalloped edge.
Place the tart in the oven and bake until the sides have risen slightly and the tart is golden brown, about 25 minutes. Check the bottom of the tart by lifting it slightly off the parchment paper using an offset spatula. You want to be sure the bottom is fully baked or the tart will be soggy. Remove from the oven and cool on a wire rack. Use a pastry brush to glaze the tart with the apricot glaze. This will add shine and sweetness to the baked tart. It is best to serve this tart within a few hours of removing it from the oven.
VARIATION: If you blind bake the dough, you can cover it with fresh raspberry jam and top with fresh raspberries as another alternative.
Mix the apricot jam with the water in a small microwaveable bowl and heat on high power or in a non-reactive 1-quart heavy-bottomed saucepan over medium heat until liquid. Brush it on with a pastry brush. The glaze can be stored in the refrigerator in an airtight container for up to 3 days.
I use glaze to give a professional finish to a tart or cake. You can make almost any kind of fruit glaze you like using any flavor of jam. I use apricot because it is clear and has a neutral flavor. You may have to adjust the amount of water based on the consistency of the jam. Heat it until it is liquid enough to apply it with a pastry brush.
Recipe courtesy Jacques Torres Chocolate, MrChocolate