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 evenly into the crust, then crumble the remaining dough on top to cover the caramel layer. Sprinkle lightly with sea salt, and remember that there's salt in the caramel sauce, too :)
Return to the oven and continue baking for an additional 25-30 minutes or until golden brown and the caramel is bubbly. If the middle jiggles a little bit, this is okay - it will continue to cook as it cools. Cool completely, then refrigerate for at least an hour before cutting into squares.