Preheat your oven to 350°F (175°C) and line a 9x13 inch baking pan with parchment paper.

In a large mixing bowl, combine all-purpose flour, granulated sugar, and salt. Cut in the cold butter until the mixture resembles coarse crumbs.

Press about two-thirds of the crumb mixture into the bottom of the prepared baking pan. Bake for 15 minutes until lightly golden.

In a separate bowl, toss sliced mixed apples with brown sugar, cinnamon, nutmeg, cornstarch, lemon juice, and vanilla extract.

Layer the apple mixture evenly over the baked crust. Crumble the remaining flour-butter mixture on top.

Bake for an additional 35–40 minutes until the topping is golden brown and the apples are tender.

Let the bars cool completely in the pan before slicing.