Chocolate Chip Cookie Base

1. Preheat oven to 350°F. Line a 9×13 pan with aluminum foil and coat with nonstick spray. Set aside.
2. In the bowl of your stand mixer fitted with the paddle attachment mix the butter and both sugars on medium-high for 2 minutes until incorporated.
3. Turn the mixer down to medium and add in the eggs, vanilla, baking soda and salt and mix for 1 minute, scraping the sides of the bowl as necessary.
4. Turn the mixer to low and add in the flour until just incorporated.
5. Stir in the chocolate chips.
6. Spread the cookie dough in the prepared pan and bake for 20-25 minutes until the edges are lightly golden and the center is almost set.
7. Remove the pan from the oven and place on a wire rack to cool slightly while you prepare the brownie layer.

Brownie Layer

1. In a medium pot on medium-low heat melt the butter. Add in the chocolate chips and stir constantly until melted and smooth. Remove the pot from the heat to cool slightly. In a medium bowl whisk together the eggs, sugar, salt and vanilla.
2. Whisk the egg mixture into the chocolate mixture.
3. Finally stir in the cocoa powder and then the flour until smooth.
4. Pour the brownie batter on top of the cookie layer evenly. Bake for 20-25 additional minutes until a toothpick inserted halfway between the center and the edge comes out clean.
5. Allow the bars to cool for 15 minutes on a wire rack and then place in the refrigerator to cool completely.

Cookie Dough Layer

1. In the bowl of your stand mixer fitted with the paddle attachment mix the butter and sugars on medium speed for 2 minutes. Add in the milk, vanilla and salt and mix for 30 seconds more. Turn the mixer to low and add in the flour until just combined and finally the chocolate chips.
2. When the cookie and brownie bars have cooled completely carefully spread the cookie dough on top using an off-set spatula.
3. Chill the bars for at least another hour before cutting into small bars.