Preheat oven 350 F.
Line a 8 X 8 pan with grease parchment paper, set aside.
To make the chocolate chip cookies dough, in a large bowl cream together butter, brown sugar and white sugar.
Beat in egg and vanilla extract.
Stir in flour, baking soda and salt until well combined.
Fold in chocolate chips. Set aside.
To make the brownie batter, in a large bowl cream together butter, brown sugar, and white sugar.
Beat in eggs and vanilla extract.
Stir in cocoa powder until combined.
Stir in flour and salt until all flour is incorporated.
Fold in mini chocolate chips if using.
Spread brownie batter into prepared pan into an even layer.
Drop the cookie dough by the spoonful over the batter until covered.
Stick additional chocolate chips into the cookie dough.
Bake for 35-40 minutes. (I prefer to remove them from the oven a bit early since I prefer my cookies a little on the undercooked side.) Remember it will continue to cook as it cools so be careful not to overbake. Check it at the 30 minute mark.
Remove from oven and place on a cooing rack to finish cooling.
Once cooled, cut into squares and serve.
Store in airtight container.