Brown the butter in a saucepan. Stir often.
Pour half into one mixing bowl. Let it cool.
Add cocoa powder, sugars, and vanilla. Mix well.
Beat in eggs. Stir until fully combined.
Fold in flour and salt. Set aside brownie batter.
Use other half of butter for cookie dough.
Beat butter with sugars in another bowl.
Add egg and vanilla. Mix until fluffy.
Stir in flour, salt, and baking soda.
Fold in chocolate chips evenly.
Line baking pan with parchment paper.
Spread brownie batter at the bottom.
Drop spoonfuls of cookie dough on top.
Gently smooth the top with spatula.
Bake at 350°F (175°C) for 30–35 minutes.
Cool completely on a wire rack before slicing.