“A co-worker couldn’t decide on her favorite for her birthday treat, brownies or chocolate chip cookies, so she said I should just pick one. On the way home I thought this up and couldn’t find it on Allrecipes so I created it. These go quickly; I usually make a double batch in a jelly roll pan.”

Ingredients

Cookie Layer:

• 1/2 cup butter, softened
• 1/2 cup light brown sugar
• 1/4 cup white sugar
• 1/2 teaspoon vanilla extract
• 1 egg
• 1 1/4 cups all-purpose flour
• 1/2 teaspoon salt
• 1/2 teaspoon baking soda
• 1 cup semisweet chocolate chip

Brownie Layer:

• 1 cup white sugar
• 1/2 cup butter, melted
• 1 teaspoon vanilla extract
• 2 eggs
• 1/3 cup cocoa powder
• 1/2 cup all-purpose flour
• 1/4 teaspoon baking powder
• 1/8 teaspoon salt

Directions

Preheat oven to 350 degrees F (175 degrees C). Grease a 9×13-inch baking dish.
Beat softened butter, light brown sugar, 1/4 cup white sugar, and 1/2 teaspoon vanilla extract together in a large bowl until creamy. Add 1 egg; beat until light and creamy, about 2 minutes.
Whisk 1 1/4 cups flour, 1/2 teaspoon salt, and baking soda together in a bowl. Gradually stir flour mixture into butter mixture until dough is combined. Stir chocolate chips into dough. Spread dough into the bottom of the prepared baking dish to cover completely.
Stir 1 cup white sugar, melted butter, and 1 teaspoon vanilla extract together in a bowl; add 2 eggs and beat well. Mix cocoa powder into butter mixture until well-combined. Stir 1/2 cup flour, baking powder, and 1/8 teaspoon salt into cocoa mixture until batter is combined. Pour brownie batter over cookie dough and spread to cover completely.
Bake in the preheated oven until a toothpick inserted into the center of the brookies comes out clean, 20 to 25 minutes. Cool completely before cutting into bars.

From: http://allrecipes.com/recipe/238654/brookies-brownie-cookies/