Preheat the oven to 425ºF (220ºC).

Melt the butter in a large skillet over medium-high heat.

Add the apples and sugar. Cook, stirring a few times, until the sugar has melted, and apples begin to caramelize slightly, 3 to 4 minutes.

Stir in the lemon zest, juice, and cinnamon. Cook for 1 minute.

Reduce the heat to medium-low. Stir in the flour, and cook until the mixture has thickened, 1 to 2 minutes more.

Roll one of the piecrusts, on a lightly floured counter, out into a 12-inch by 15-inch rectangle (30-cm by 38-cm). Place the dough into a 9-inch x 13-inch x 1-inch sheet pan (rimmed baking sheet). Gently press the dough into the bottom, and up the sides, folding an overhang inside the pan (watchthis video to see how to roll out the crust).

Spread the filling evenly across the crust.

Roll out the remaining crust 1/8-inch thick. Use a cookie cutter to press out desired shapes.

Evenly sprinkle the crumb topping over the apples. Arrange the cutout pieces of dough as desired. Brush the cutouts and edges of the crust with the egg wash.

Bake 20 minutes. Reduce oven to 350ºF (180ºC). Bake 20 to 25 minutes more, until filling is bubbling, and crust is deep golden.

Let cool completely before cutting & serving.