Preheat the oven to 350 degrees F. Line baking sheets with silpat liners or parchment paper. Set aside.
For the brownie cookie batter, in a medium bowl with a handheld electric mixer (or in the bowl of an electric stand mixer), beat the butter, granulated sugar and brown sugar together until smooth and creamy, 1-2 minutes. Add the egg, yolk and vanilla and beat the mixture for 2-3 minutes until light in color.
In a separate small bowl, whisk together the flour, cocoa, soda and salt. Add the dry ingredients to the batter and mix until combined. Cover and refrigerate while making the chocolate chip cookie batter.
For the chocolate chip cookie batter, in the bowl of an electric stand mixer or with a handheld electric mixer, cream together the butter, granulated sugar, and brown sugar until smooth, 1-2 minutes.
Blend in the egg, egg yolk and vanilla, mixing for 2-3 minutes until the batter is very light in color. In a separate small bowl (you can use the same one as the brownie batter dry ingredients), whisk together the flour, baking soda, and salt. Add the dry ingredients to the batter with the chocolate chips and mix until no dry streaks remain and the chocolate chips are evenly distributed.
Portion both sets of dough into about 4 dozen equal pieces; they will be small teaspoon or so sized balls (if you want to be super precise, I weigh about .5 ounce balls for the brownie batter and .65 ounce balls for the chocolate chip cookie batter).
Grabbing one chocolate chip cookie ball and one brownie batter ball, press them together and use your hands to gently form into a cookie shape, flattening and turning to smooth the edges and form a flattish but still thick cookie shape; they'll spread out while baking. See the simple picture tutorial below the recipe, if needed.
Bake the cookies on the prepared baking sheets for 8-10 minutes. Don't overbake or they will be dry and crunchy - underbake just slightly for a soft, chewy texture. It's ok if the chocolate side crackles just a bit. Remove from the oven and let the cookies cool on the pan for 1-2 minutes before scooping onto a cooling rack to cool completely.
Amount Per Serving
Calories 297Calories from Fat 117
% Daily Value*
Saturated Fat 8g50%
Trans Fat 1g
Vitamin A 355IU7%
Vitamin C 1mg1%
* Percent Daily Values are based on a 2000 calorie diet.