Weigh out the ingredients
You'll need flour, cocoa powder, butter, chocolate, brown sugar, granulated sugar, egg, egg yolk, salt, and vanilla.
Melt chocolate & butter
In a small bowl, add the chocolate and butter. Place over a small saucepan of simmering water, and stir often until fully melted. Remove the chocolate butter mixture from the double boiler and allow to cool for a few minutes.
Meanwhile, in a large bowl, add the sugars, eggs, and vanilla.
Combine sugars & eggs
Using an electric mixer, beat on high speed for about 3-4 minutes until the mixture has doubled in size.
Beat until doubled in size
While mixing on low speed, slowly pour in the chocolate butter mixture. Continue mixing until fully combined.
Mix in the chocolate mixture
Add the flour, cocoa powders, and salt, and use a rubber spatula to gently fold until mostly combined.
Fold in the dry ingredients
Lastly, fold in the chopped chocolate until evenly dispersed.
Fold in the chopped chocolate
Pour the brownie batter into the prepared pan and smooth out the top. Add more chopped chocolate on top, if desired. Bake the brownies for about 28 minutes.
Allow them to cool completely in the pan before removing. Cut into 8 triangles, top with flaky sea salt, and enjoy!