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.
I modified it a bit to avoid it getting soggy in the center (by brushing butter in the middle). For details and photos, check my blog: http://afewminutesatatime.wordpress.com/2013/03/07/easy-apple-tarts/
The simplicity of this recipe made it 100% worthwhile. It was delicious, and impressed the guests! I made two at a time. Cooking it at 6200ft. of altitude provided one single challenge: getting the apples to caramelize! We cooked it at least 40 minutes at 375.
I wonder if this would work using lemon curd instead of the apricot preserves. Lemon sounds like it would go well here.