Make the brownie batter:

1. Preheat your oven to 350°F. Butter an 8x8 inch pan and line the bottom and sides with parchment paper. Leave a bit of extra parchment paper hanging over the sides of the pan to make it easier to pull the baked brownies out.
2. In a small pot, melt butter on medium heat until fully melted and sizzling.

   - 1/2 cup (115g) unsalted butter

3. 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.

   - 1/2 cup (100g) dark brown sugar, 1/2 cup (100g) granulated sugar

4. Whisk in the eggs and vanilla.

   - 2 large eggs, 1 teaspoon pure vanilla extract

5. Add in flour, cocoa powder, salt, and the chopped chocolate bar. I like to reserve a few pieces from the chocolate bar to sprinkle on top of the layered brownie later. Mix together until just combined. Take care not to overmix! 

   - 1/2 cup (65g) all-purpose flour, 1/2 cup (40g) unsweetened cocoa powder, 1/4 teaspoon salt, 3.5 oz (100g) 70% cocoa chocolate bar

6. Pour the brownie batter into your prepared baking pan. Spread into an even layer and set aside to prep the cookie dough.
7. You can use the same bowl to make the cookie dough - just give the bowl a light wipe down so it's relatively clean - it doesn't have to be spotless though!

Make the cookie dough:

1. Heat butter in a pot over medium heat until melted.

   - 6 tablespoons (90g) unsalted butter

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

   - 1/3 cup (67g) dark brown sugar, 1/4 cup (50g) granulated sugar

3. Add the egg and vanilla and whisk until smooth.

   - 1 large egg, 1 teaspoon pure vanilla extract

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

   - 1 cup (130g) all-purpose flour, 1 tablespoon cornstarch, 1/2 teaspoon baking soda, 1/4 teaspoon salt

5. Fold in the chocolate chips.

   - 3/4 cup (130g) semi-sweet chocolate chips

6. 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.
7. 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.
8. 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, close the door, then give the pan about 5 or 6 firm bangs on your counter. The center should deflate as you do this.**
9. Place the brownies back in your oven and bake for another 8-12 minutes or until the cookie dough has evenly browned on top.
10. Cool the brownies completely in the pan before pulling them out and slicing. Sprinkle some flaky sea salt on top if desired before serving.