Preheat the oven to 350°F. Line a 9x13-inch baking pan with foil, leaving a 2-inch overhang on the two short sides of the pan. Grease the foil with cooking spray.
In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter and sugar until light and fluffy, about 2 minutes.
Add the eggs one at a time, beating between each addition, then add the vanilla extract and beat until combined.
Add the flour and salt and beat just until the dough comes together. (It will be very sticky.) Transfer the dough to the prepared baking pan, pressing it into an even layer with your hands. (If your hands stick, spray them lightly with cooking spray.)
Bake the cookie bars for about 25 minutes or until they’re golden brown around the edges. Remove the cookie bars from the oven and allow them to cool completely in the pan. While the bars cool, make the frosting.