Apple Pie Bars

Crust:

3 sticks unsalted butter, softened
3/4 cup sugar
3 cups all-purpose flour
1/2 teaspoon  salt

Filling:

6 tablespoons unsalted butter
1/2 cup light brown sugar
12 Granny Smith apples (about 6 pounds)—peeled, cored and thinly sliced
1 tablespoon cinnamon
1/4 teaspoon freshly grated nutmeg
1/2 cup water, if necessary

Topping:

3 cups quick-cooking oats
2 cups all-purpose flour
1 1/2 cups light brown sugar
1 1/4 teaspoons cinnamon
1/2 teaspoon baking soda
1/2 teaspoon salt
3 sticks (12 ounces) unsalted butter, cut into 1/2-inch cubes and chilled
3/4 cup chopped pecans (optional)

Make the Crust:

• Preheat the oven to 375°. 
• Line a 15-by-17-inch rimmed baking sheet with parchment paper. 
• In a standing mixer fitted with the paddle attachment, beat the butter with the sugar at medium speed until light and fluffy, about 2 minutes. At low speed, beat in the flour and salt until a soft dough forms.
• Press the dough over the bottom of the prepared pan creating an even layer.
•  Bake in the center of the oven for about 20 minutes, until the crust is golden and set. Let cool on a rack.

Make the Filling:

• In an extra large skillet, melt 6 tablespoons of the butter with 1/2 cup of the light brown sugar. 
• Add the apples to the skillet and cook over high heat, stirring occasionally, until softened, about 10 minutes. 
• Stir the cinnamon and nutmeg.
• Cook until the apples are caramelized and very tender and the liquid is evaporated, about 10 minutes longer;
•  scrape up any bits stuck to the bottom of the skillet and if necessary, add up to 1/2 cup of water to prevent scorching. 
• Let cool. 

Make the Topping:

• In a large bowl, mix the oats with the flour, light brown sugar, cinnamon, baking soda and salt. 
• Using a pastry blender to cut in the butter until the mixture resembles coarse meal.
•  Stir in the pecans and press the mixture into clumps.

Assemble and Bake:

• Spread the apple filling over the crust. 
• Scatter the crumbs on top, pressing them lightly into an even layer. 
• Bake in the center of the oven for 1 hour, until the topping is golden; rotate the pan halfway through baking.
•  Let cool completely on a rack before cutting into 2-inch bars.