In a food processor, add the flour, sugar, and salt. Pulse until blended.

Add the butter and pulse until blended.

While pulsing, add the water a little at a time until the dough comes together in smooth dough.

Transfer the dough to a lightly floured surface and knead four or five times.

Divide the dough into two equal portions and pat into rectangles.

Wrap in plastic wrap and refrigerate for at least two hours to overnight.

Preheat the oven to 375 degrees F.

Roll out one pie crust onto a lightly floured surface into a 9x13-inch rectangle.

Press the crust into the bottom of a 9x13-inch baking dish with the edges curved slightly up the sides.

In a large mixing bowl, whisk the white sugar, flour, and apple pie spice together.

Toss Granny Smith apples and gala apples in the sugar mixture until they are evenly coated.

Add the vanilla extract, drizzling over the top, and toss again.

Spread the apple mixture evenly over the pie crust, leaving the edges of the dough open.

Roll out the remaining pie crust into a 9x13-inch rectangle.

Place it over the apple layer, folding the edges over the apples to completely cover them and pressing into the edge of the bottom crust.

If desired, brush the top of the pie crust lightly with water.

Bake until the crust is lightly browned or about 45 to 50 minutes.

Remove bars from the oven and allow to cool slightly or around 20 to 30 minutes.

In a separate bowl, whisk together the powdered sugar, milk, and vanilla extract until smooth.

Drizzle the topping over the bars.

Slice into squares and serve warm.