Prepare the Salted Caramel Sauce
Preheat oven to 325°F. Line an 8×8-inch baking pan with aluminum foil so that the edges of the foil overhang two sides of the pan, and spray the foil with cooking spray.
In a medium bowl, whisk together the flour, baking soda, and salt.
In the bowl of a stand mixer fitted with the paddle attachment or in a large bowl with a hand mixer, on medium speed, beat together the butter, brown sugar, and granulated sugar.
Beat in the egg, yolk, and vanilla until just combined.
Reduce the mixer speed to low, and add the dry ingredients to the wet ingredients until just combined - do not overbeat.
Stir in the white chocolate chips.
Dampen your fingers, and press half of the dough into the bottom of the prepared pan.
Pour the Salted Caramel Sauce over the dough and spread evenly.
Drop the remaining dough in clumps over the caramel – the dough will bake together.
Bake for 30-35 minutes until a toothpick comes out clean. (I actually had to bake mine a few minutes longer, and they were still fairly gooey from the extra caramel.)
As soon as the bars come out of the oven, sprinkle the top with the sugar and sea salt.
Allow the pan to cool on a wire rack for 15 minutes before carefully removing the bars from the pan and peeling off the foil.
Cool completely before slicing.