Preheat oven to 325° F.

In a large bowl, combine the butter, sugar, and powdered sugar. Using a mixer on medium speed, mix until creamy. Add the vanilla and mix until combined. Sift the flour into the butter mixture and beat on low speed until you have a smooth soft dough.

Spray a 9x9 inch baking pan lightly with non-stick cooking or baking spray. Press one-third of the dough evenly into the pan to form a bottom crust. Wrap remaining dough in plastic wrap and chill in refrigerator.

Bake crust until firm and the edges are a pale golden brown approx 20 minutes. Transfer pan to a wire rack and let cool about 15 minutes.

Sprinkle caramel bits evenly over the crust. Sprinkle chocolate chips evenly over that.

Remove the chilled dough from the refrigerator and crumble it evenly over the caramel bits and chocolate chips. Sprinkle a few chocolate chips evenly over the top of the crust.

Return the pan to the oven and bake until the caramels is melted and the crumbled shortbread topping is firm and lightly golden, about 25 - 30 minutes.

Let cool before cutting into squares.