Dulce de Leche is possibly my favorite food. This is the most-requested recipe I make... adapted from Gooey Caramel Butter Bars found in Jill O’Conner’s Sticky, Chewy, Messy, Gooey cookbook. They are very rich, so you can cut them into smaller portions to serve more than 24. —Bourbon and Brown Sugar
In a the bowl of a standing mixer, combine the butter and sugars, and beat until creamy. Add the vanilla, and mix until combined. Add the flour into the butter mixture and mix on low speed until a smooth, soft dough forms.
Line a 9 x 13 pan with parchment paper. Press about half of the dough evenly into the pan to form a bottom crust. Place the remaining dough aside in the refrigerator to chill. Bake the bottom crust until firm and the edges are a pale golden brown, 20 to 25 minutes.
When the bottom crust is finished, let it rest for about five minutes. Microwave the dulce de leche for about 30 seconds so that it softens a bit and is easy to spread. Spoon the dulce de leche onto the bottom crust, and spread it out evenly.
Remove the remaining chilled dough from the refrigerator and crumble it evenly over the dulce de leche layer. Sprinkle the sea salt evenly over the topping. Return the pan to the oven and bake it until the filling is bubbly and the crumbled shortbread topping is firm and lightly golden brown, about 30 minutes. Let it cool completely.