Pour the water into a medium saucepan. Pour the sugar into the center of the pan, making sure none of the sugar crystals hit the sides. Add the corn syrup.
Place pan over medium heat, leaving it alone for the first 5 minutes or until it the color begins to turn yellowish. Once you see some color, gently swirl the pan around occasionally as it boils. Continue boiling until the caramel reaches a golden amber color, about 5 to 10 minutes.
Remove pan from the heat and carefully whisk in the heavy cream. Caramel will sizzle and bubble up. Stir in the salt, and continue whisking until caramel is smooth. If needed, return pan over medium-low heat, stirring until caramel is smooth. Transfer to dish or glass measuring cup to cool completely. Caramel will continue to thicken as it cools.
Make the Cookie Dough:
Preheat the oven to 350ºF and line an 8-inch square baking pan with parchment paper, leaving extra overhang on both sides for easy removal.
In a medium saucepan, melt the butter over medium-low heat. As the butter melts, it’ll start to foam, then turn a clear golden color. Continue to stir the butter, scraping up any browned specks from the bottom of the pan as it starts to brown. It should have a nutty aroma. Once browned and nutty, transfer to a large bowl; cool slightly.
Whisk the flour, baking soda, salt, and cornstarch together in a medium bowl; set aside.
Using a fork, vigorously stir both sugars into the brown butter until smooth and combined, about 1 minute. Stir in the eggs and vanilla. Add the dry ingredients, stirring until just incorporated. Stir in the chocolate chips.
Press half of the dough into the baking dish. Pour caramel on top, spreading out evenly. Take chunks of the remaining dough, flatten them slightly, and layer them side by side on top of the caramel. Try to cover as much of the caramel as possible.
Bake for 20-25 minutes, or until edges are lightly golden. Cool completely*.
Run a knife along the edges of the pan to loosen the bars. Using the parchment overhang, gently lift the bars out of the pan and cut into squares. Eat immediately.
To store leftover bars, I recommend wrapping each bar individually in plastic wrap to prevent the caramel from running.
Notes
*Cooling process can be sped up by placing the baked bars in the refrigerator.