Preheat your oven to 350°F. Butter an 8x8 inch pan and line the bottom and sides with parchment paper.

In a small pot, melt butter on medium heat until fully melted and sizzling.

Pour the butter into a large bowl and immediately add in the brown and granulated sugars while the butter is still hot. Mix to combine - it will be grainy.

Whisk in the eggs and vanilla.

Add in flour, cocoa powder, salt, and the chopped chocolate bar. Mix together until just combined.

Pour the brownie batter into your prepared baking pan. Spread into an even layer and set aside to prep the cookie dough.

Heat butter in a pot over medium heat until melted.

Pour the butter into your bowl and add brown and granulated sugars. Mix to moisten the sugars.

Add the egg and vanilla and whisk until smooth.

Add flour, cornstarch, baking soda, and salt. Mix together until streak free.

Fold in the chocolate chips.

Using a 1.5 tablespoon cookie scoop or 2 spoons, take chunks of cookie dough and dollop them over the brownie batter in your prepared pan.

Gently press each blob of cookie dough down to wedge it into the brownie batter and roughly even out the top. Sprinkle over some more chopped chocolate and chocolate chips on top.

Bake the brownies in the center of your preheated oven for 25 minutes. After the 25 minutes, take the pan of brownies out of the oven and give the pan about 5 or 6 firm bangs on your counter.

Place the brownies back in your oven and bake for another 8-12 minutes or until the cookie dough has evenly browned on top.

Cool the brownies completely in the pan before pulling them out and slicing. Sprinkle some flaky sea salt on top if desired before serving.