These snickerdoodle bars are slightly crispy on the exterior and wonderfully chewy on the inside. They are chock full of cinnamon and cinnamon morsels, making them doubly delicious. They're easy to make and perfect for the holidays.
Heat oven to 350F with rack on lower middle position. Line a 13x9 inch baking pan with foil, making a foil "sling" on either side past the pan for easy lifting of the whole dessert after baking. Set aside.
In a bowl, combine the flour, baking powder, salt, and cinnamon. Set aside.
In the bowl of a stand mixer, with paddle attachment, beat the softened butter until creamy. Add in the sugars and beat until fully incorporated. Beat in the eggs and vanilla just until combined. Switch to low speed, and gradually add in the dry ingredients just until combined. Do not over beat.
Using a rubber spatula, transfer two-thirds of the batter into foil-lined pan. Spread batter evenly. Sprinkle the cinnamon sugar mixture evenly over the batter. Distribute teaspoon-sized amounts of remaining batter evenly over the cinnamon sugar mixture. (It will not cover all the cinnamon sugar layer, but that is ok. Using damp fingers will help distribute the batter with ease.)
Bake 20-25 min or just until golden brown and toothpick inserted in center comes out almost clean. A few tender crumbs attached are perfect. Allow to cool completely. Stir together the glaze ingredients until it's a nice consistency for drizzling. Add a bit more powdered sugar or milk, according to how thick/thin you want it. Remove entire bar dessert using the foil sling and transfer to a cutting board. Drizzle icing on top. Cut and serve.