Preheat oven to 350 degrees.
To prepare crust, mix flour, sugar, salt, and baking powder in the bowl of a food processor. Cut butter into chunks; add to processor and pulse until you have pea-sized crumbles. Pour into a medium bowl and gently mix in beaten egg.
Spray a 9x13 baking dish with non-stick cooking spray. Gently pat about 2/3 of the crumb mixture onto the bottom of the dish. Set aside.
To prepare apple filling, combine flour, sugar, and cinnamon. Toss with apples and spread apples out on prepared crust. Sprinkle reserved crust mixture over apples evenly and bake in preheated oven for 40 minutes. When finished, allow to cool completely.
To prepare glaze, whisk together powdered sugar, almond extract, and enough milk to achieve desired consistency. Place glaze in a Ziploc bag and cut off a very small portion of one of the corners. Drizzle glaze over cooled pastry and allow to harden (you can place it in the freezer to hurry things along). Cut into bars and serve.