1. Preheat the oven to 350°F (175°C). Line a 9×13 inch pan with parchment paper.
2. In a food processor, pulse together the flour and granulated sugar. Add the cold, cubed butter and pulse until the mixture resembles coarse crumbs.
3. Press two-thirds of the crumb mixture into the bottom of the prepared pan to form the crust.
4. In a large bowl, toss the sliced apples with lemon juice, brown sugar, cinnamon, nutmeg, and salt until well coated.
5. Spread the apple mixture evenly over the crust in the pan.
6. In a small saucepan, combine the cornstarch and apple cider. Cook over medium heat, stirring constantly, until the mixture thickens. Remove from heat and stir in the vanilla extract.
7. Pour the thickened apple cider mixture over the apple layer in the pan.
8. Crumble the remaining flour mixture evenly over the top of the apple cider layer.
9. Bake in the preheated oven for 45-50 minutes, or until the top is golden brown and bubbly.
10. Allow the bars to cool completely in the pan before slicing into bars.
11. Serve and enjoy these delicious flaky apple pie bars as a delightful dessert or snack!
