Preheat your oven to 350°F (175°C). Grease or line the 9x13 inch baking pan with parchment paper.
In a large mixing bowl, melt the 1 cup of butter for the brownie layer. Stir in the granulated sugar until well combined.
Add the eggs, one at a time, mixing well after each addition. Stir in the vanilla extract.
In a separate bowl, whisk together the flour, cocoa powder, and salt. Gradually add this dry mixture to the wet ingredients, stirring until just combined.
Fold in the chocolate chips. Pour the brownie batter into the prepared baking pan, spreading it out evenly.
Bake for 25-30 minutes or until a toothpick inserted into the center comes out with a few moist crumbs. Let cool completely in the pan.
While the brownies are cooling, prepare the cookie dough layer. In a mixing bowl, cream together the softened butter, brown sugar, and granulated sugar until fluffy.
Mix in the vanilla extract, then add the flour and salt. Stir until the dough is fully combined.
Add the milk and chocolate chips, mixing until evenly distributed.
Once the brownie layer is completely cool, spread the cookie dough over the top evenly.
Refrigerate for at least 30 minutes to allow the cookie dough to firm up before cutting into squares.
Slice into 12 squares and serve chilled or at room temperature. Enjoy your delicious Chocolate Chip Cookie Dough Brownies!