• Preheat the oven to 350 degrees. Spray a 9X13 inch baking dish with nonstick cooking spray. Set aside.

Make the Cookie Layer:

• In a large mixing bowl, cream together butter, brown sugar, granulated sugar, and vanilla using an electric mixer on medium speed, until the mixture is well combined and creamy.
• Add the egg and continue to cream the mixture until it becomes light and fluffy, or for about 2 minutes. Set mixture aside.
• In a medium mixing bowl, whisk together flour, salt, and baking soda until evenly combined. Gradually mix flour mixture into butter mixture until just combined. Mix in chocolate chips.
• Spread cookie dough evenly into the bottom of the prepared baking dish covering the pan completely. Set aside.

Make the Brownie Layer:

• In a medium mixing bowl, mix together granulated sugar, melted butter, and vanilla. Add eggs and mix until completely combined.
• Stir cocoa powder into sugar/butter mixture and mix until well combined. Add flour, baking powder, and salt and mix until incorporated.
• Pour brownie mixture evenly over cookie dough, covering the dough completely.
• Bake in preheated oven until a toothpick inserted into the center comes out with just a few moist crumbs (not batter, just a couple of crumbs), about 40-45 minutes. Allow to cool completely. The brownies need this time to finish setting. I prefer to cool them then refrigerate them overnight before serving.