Preheat the oven to 425ºF (220 ºC).
Melt the butter in a small skillet over medium-high heat.
Add the apple slices and sugar. Cook, stirring a few times, until the sugar has melted, and apples begin to caramelize slightly, 2 to 3 minutes.
Stir in the lemon juice, and cinnamon. Cook for 1 minute.
Reduce the heat to medium-low. Stir in the flour, and cook until the mixture has thickened, about 1 minute more.
Roll the piecrusts, on a lightly floured counter, out into an 11-inch (28-cm) circle. Drape the dough over a 6-inch (15-cm) round tart pan. Gently press the dough into the bottom, and up the sides. Trim the edges of the dough (there will be a lot left over).
Re-roll the scraps on a lightly floured counter, if necessary, to 1/8-inch thick. Use a cookie cutter to press out desired shapes. Arrange over the top in desired pattern.
Brush the crust with the egg wash. Sprinkle a bit of sugar on top.
Bake 10 minutes. Reduce oven to 350ºF (180ºC). Bake 25 minutes more, until filling is bubbling, and crust is golden. Let cool completely before cutting & serving.