Brown your butter:Add butter to a saucepan and place over medium heat. The butter will begin to crackle, and start to foam. Whisk constantly during at this point. After a couple of minutes, the butter will begin turn a golden amber color on the bottom of the saucepan. Continue to whisk and remove from heat as soon as the butter begins to brown. Immediately transfer the butter to a bowl to prevent burning. Set aside to cool for 10 minutes or until cool enough to touch. Preheat oven to 350°F. Prepare baking pans with non-stick spray, or other pan release method.
In a medium bowl whisk flour, cornstarch, baking powder, and salt. Set aside.
In a separate large bowl, add your browned butter and brown sugars. Whisk you have a smooth mixture with no lumps.
Next add your eggs and vanilla. Whisk the mixture vigorously making sure the eggs are fully combined. The mixture will lighten in color.
Now add you dry ingredients to the wet. Mix just until the flour has combined. Do not overmix. Fold in your pecans
Add the batter to your prepared dish and smooth into an even layer.
Drizzle your caramel sauce evenly over the batter.
Bake for about 35 minutes at 350F. The cookie bars are done when the edges are set and golden brown and a toothpick or skewer inserted into the center comes out mostly clean. Sprinkle with flaked salt.Let the cookie bars cool in the pan for about an hour before removing and cutting.