Preheat your oven to 350?. Spray a 9?13 metal pan with nonstick spray and line with parchment paper.

Make the Chocolate Chip Cookie Dough: Melt the butter in a large mixing bowl. Whisk in the sugars. Add the eggs and vanilla, and whisk until smooth and combined, about 30-45 seconds. Stir in the dry ingredients, then the chocolate chips last. Divide the dough into two equal halves. Press half of the dough into the prepared pan, then lift out that piece of parchment paper and replace with a new piece. Set your layer of cookie dough aside and leave the rest in the bowl for later.

Brown the Butter: Add cubed butter to a medium saucepan over medium heat. Melt the butter, stirring occasionally. Once melted, turn the heat to medium-low, and continue cooking the butter, stirring frequently until it turns a deep golden shade with a nutty aroma (about 3-6 minutes).

Make the Brownie Batter: Stir in the chopped semi-sweet chocolate into the browned butter until melted. Whisk in the vegetable oil and cocoa powder. Set aside to cool slightly. In a large mixing bowl, add the eggs, egg yolk, and granulated sugar. Whisk for about 1-2 minutes, until the sugar is fully dissolved. Whisk in the powdered sugar, vanilla, and salt. Ensure the chocolate mixture is not piping hot and whisk it into the bowl of eggs/sugar. Fold in the flour and espresso powder, then the chocolate chips.

Assemble: Spread slightly more than half the brownie batter in the bottom of your lined pan. Lay the sheet of cookie dough on top. Spread the remaining brownie batter on top. Form large, thick discs with the remaining cookie dough and set them on top of the batter. Press extra chocolate chips into any bare spots if desired.

Bake: Bake the assembled brookies for 38 to 44 minutes until golden and shiny on top. A toothpick inserted into the center of a brownie spot should have some moist crumbs but not wet batter.

Serve & Store: Allow bars to cool in the pan on a wire rack for about 1 ? 2 hours before slicing and serving. If desired, sprinkle with flaky sea salt. Store leftover bars in an airtight container at room temperature for 3-4 days.