Roll puff pastry into a 14-by-16-inch rectangle on a lightly floured surface. Cut a 1-inch-wide strip from each side of dough. Brush edges with egg wash, and top with cut strips to form a crust. Prick middle of dough all over with a fork, and transfer to a parchment-lined baking sheet. Refrigerate for 30 minutes.
Preheat oven to 400 degrees. Spread applesauce onto middle of dough using an offset spatula. Arrange apple wedges over applesauce in 3 tightly overlapping rows. Brush apples with melted butter. Brush crust with egg wash, and sprinkle entire surface with sanding sugar. (Unbaked tart can be frozen for up to 3 days.)
Bake until edges start to puff, about 20 minutes. Reduce heat to 375 degrees, and bake, rotating halfway through, until pastry is dark golden brown and apples have caramelized, 25 to 30 minutes more. Transfer sheet to a wire rack, and let cool for 10 minutes.
Warm apricot preserves and water in a medium saucepan over medium heat. Brush apples with warm apricot preserves. Dust with confectioners' sugar if desired, and cut into squares using a pizza wheel or a knife. Serve warm with whipped cream if desired.
Once assembled, this tart can be frozen for up to three days. Simply bake it straight from the freezer as instructed.