Preheat oven to 325 degrees F. Line a 13x9" baking pan with foil, extending the sides of the foil over the edges of the pan. Spray the foil liberally with cooking spray and set aside.

In the bowl of a stand mixer fitted with the paddle attachment, beat together the butter and sugar until creamy and fluffy, about 2 minutes. Beat in the powdered sugar and vanilla. Lastly, beat in the four (4) cups of flour until a soft dough has formed. Press HALF of the dough evenly into the bottom of the prepared pan. Refrigerate the remaining dough.

Bake the crust for 15 minutes. Remove from the oven but keep the oven on. Pour the caramel sauce evenly over the bar base, then pour on the Biscoff spread (it helps if you microwave it for a few seconds in a separate bowl to make it smoother and thinner). Crumble the remaining dough evenly over the top, trying to cover the sauce filling as much as possible. Top liberally with the toffee bits.

Return to the oven and continue baking for an additional 25-30 minutes or until golden brown and the caramel is bubbly. Cool completely before cutting into squares.