Apple Pie Bars

**Shortbread Layer:**

1. Preheat the oven to 350°F.
2. In a stand mixer, cream the softened butter and sugar until pale and fluffy (3-5 minutes on medium-high speed).
3. Add the flour, cornstarch, and salt. Pulse until just combined.
4. Pat the shortbread into a parchment-lined 9×13 inch pan until it forms an even layer.
5. Bake for 45-55 minutes until golden brown (check after 35 minutes if using a metal pan).
6. After baking, reduce the oven temperature to 300°F for baking the bars.

**Apple Pie Filling:**

1. While the shortbread bakes, brown the butter in a large skillet over medium heat until golden and toasty.
2. Stir in the sugars, salt, cinnamon, and vanilla.
3. Add the apple slices and lemon zest. Cook over medium heat for 8-10 minutes until slightly softened. Set aside to cool.

**Crumb Topping:**

1. In a bowl, combine flour, cinnamon, and brown sugar.
2. Pour in the melted butter and mix with a fork until large crumbs form. Set aside.

**Assembly:**

1. Spread the apple pie filling evenly over the cooked shortbread.
2. Sprinkle the crumble evenly over the apple layer.
3. Bake at 300°F for 30 minutes.
4. Increase the oven temperature to 350°F and bake for an additional 15 minutes until golden brown.

**Glaze:**

1. In a medium bowl, mix powdered sugar and vanilla. Gradually whisk in milk.
2. Once the bars are cooled, drizzle the glaze over the top using a spoon or piping bag (a Ziploc bag with the corner snipped off works too).