Make the streusel topping first: In a medium sized mixing bowl, whisk together the rolled oats, brown sugar, flour, salt and cinnamon.
1 cup Old-Fashioned Rolled Oats (not quick cook or 1-minute), 1 cup brown sugar, packed, 3/4 cup All-Purpose Flour, 1/4 tsp. salt, 1/4 tsp. cinnamon
Cut in the chilled, cubed butter or mix with fingertips until the mixture comes together in clump
1/2 cup chilled, unsalted butter cut into cubes
Cover the streusel and place in refrigerator to chill while you prepare the shortbread crust and apple pie filling.
Make the shortbread crust: In a large mixing bowl, whisk together the flour, salt and cinnamon. Set aside.
2 1/2 cups All-Purpose Flour, 1 tsp. salt, 1/2 tsp. cinnamon
In a stand mixer fitted with a paddle attachment, cream the softened butter, white sugar and brown sugar together until creamy.
1 1/4 cup softened, unsalted butter, 2/3 cup granulated sugar, 2/3 cup brown sugar, packed
Add in the vanilla and then with the mixer on low gradually add in the dry ingredients.
1 1/2 tsp. vanilla extract
Press this into a 9x13 oven safe baking dish and refrigerate for 20 minutes (don't skip this step!).
Preheat the oven to 375°F. Once chilled, bake for 18 minutes in the oven. Remove and let cool while you prepare the filling. Decrease the oven temperature to 350°F.
Place the sliced apples in a large mixing bowl and mix in the sugar, cinnamon, nutmeg.
6-8 apples (~3 lbs.) Mix of Granny Smith + Pink Lady, 1/3 cup granulated sugar, 2 tsp. cinnamon, 1/4 tsp. nutmeg (optional)
Whisk together the lemon juice and cornstarch and add to apples. (This is the thickener). Pour the apple mixture into a large saucepan over medium heat and cook for 5-8 minutes or until apples soften. Stir occasionally and add water as needed so apples don't burn or scorch pan.
1 lemon, juiced (~ 2 Tbsp.), 2 Tbsp. cornstarch*, 1/2 cup water, as needed
Layer the apples over the shortbread crust.
Top the apples with the streusel.
Bake for 30-35 minutes. Let apple pie bars cool. Slice and serve as is or with vanilla bean ice cream!