1. 1. Prepare your baking dish and oven: Preheat your oven to 375 F (190 C). Lightly grease a 9×13-inch baking dish or line it with parchment paper, leaving an overhang on the sides for easy lifting later. This prevents sticking and makes serving a breeze.

2. 2. Lay out the bottom crust: Unroll one of the refrigerated pie crusts and carefully press it into the bottom of your prepared baking dish, gently easing it up the sides slightly. If the crust tears, simply press it back together with your fingers.

3. 3. Mix the apple filling: In a large bowl, combine the peeled, cored, and thinly sliced apples with the granulated sugar, ground cinnamon, ground nutmeg, all-purpose flour, and lemon juice. Toss everything together until the apples are evenly coated with the spice mixture. The flour helps to thicken the juices released by the apples during baking, preventing a watery filling.

4. 4. Assemble the bars: Pour the apple mixture evenly over the bottom pie crust in the baking dish. Make sure the apples are spread out in a relatively even layer.

5. 5. Add the top crust and decorative touches: Unroll the second pie crust. You can either place it whole over the apple filling, gently pressing the edges to seal with the bottom crust, or cut it into strips to create a lattice top for a more decorative look. If using a whole top crust, cut a few slits in the top to allow steam to escape during baking.

6. 6. Apply egg wash and sugar (optional): In a small bowl, lightly beat the egg. Brush the top crust generously with the beaten egg. This egg wash will give the crust a beautiful golden sheen. If desired, sprinkle the coarse sugar evenly over the top crust for added sparkle and a slight crunch.

7. 7. Bake to golden perfection: Place the baking dish in the preheated oven and bake for 30-35 minutes, or until the crust is golden brown and the apple filling is bubbly. The apples should be tender when pierced with a fork.

8. 8. Cool before serving: Once baked, remove the bars from the oven and let them cool in the baking dish on a wire rack for at least 30 minutes before slicing and serving. This cooling time allows the filling to set properly, making for cleaner slices.