Preheat oven to 350°F (175°C). Grease a baking pan.
For the brownie layer: In a mixing bowl, combine melted butter and sugar. Add eggs one at a time, mixing well after each addition. Stir in flour, cocoa powder, salt, and vanilla extract. Spread the batter evenly in the prepared pan.
Bake for 20-25 minutes or until a toothpick inserted into the center comes out clean. Let it cool completely.
For the cookie dough layer: In a mixing bowl, cream together softened butter, brown sugar, and white sugar until fluffy. Add eggs and mix well. Gradually add flour, baking soda, and salt. Stir in chocolate chips.
Spread the cookie dough evenly over the cooled brownie layer. Refrigerate for at least 30 minutes before cutting into bars.