Step 1

In the bowl of an electric mixer fitted with the paddle attachment, combine the butter, brown sugar, and granulated sugar; beat until mixture is lightened. Beat in the egg and then the egg yolk. Add the vanilla extract, mixing until well-blended.

Step 2

Scrape down the sides of the bowl. In a medium bowl, whisk together the 2 1/4 cups flour, baking soda, and salt. Add to the creamed mixture and beat on low speed until just incorporated. Stir in the chocolate chips. Cover and set aside.

Step 3

Whisk together the sugar and cocoa in a large mixing bowl; set aside. In a microwave safe bowl, heat the butter in 30 second intervals in microwave on 100% power until completely melted (about 1 minute to 1 minute 30 seconds total). Pour butter into the bowl with sugar and cocoa; stir until smooth. Add the eggs to mixture one at a time, stirring after each addition until completely incorporated. Stir in the vanilla. Add the flour, baking powder and salt; stir until well combined. Cover and set aside.

Step 4

Preheat the oven to 375°F. Line two baking sheet with parchment paper.

Step 5

Using a small cookie scoop (4 teaspoon capacity) portion out all of the chocolate chip cookie dough onto a cookie sheet. Wash and dry the cookie scoop, then portion out the brownie dough in the same manner. (If you don’t have a cookie scoop, portion dough using measuring spoons, about 1 1/2 level tablespoons for each dough ball.)

Step 6

Press a chocolate chip cookie dough ball and brownie dough ball together and roll between your palms into a ball. Repeat with remaining dough balls. Place each dough ball about two inches apart on prepared baking sheets, and bake for 10-12 minutes or until well puffed and lightly golden on the edges of the chocolate chip cookie halves.

Step 7

Remove from oven, and let cool on baking sheets about 3 minutes before moving cookies on to cooling racks to cool completely.