1/2 brownie, 1/2 chocolate chip cookie. The best of both worlds.
In a mixing bowl, combine the flour, baking soda, and salt.
In another mixing bowl, combine the butter, brown sugar, and granulated sugar and mix well. Add the egg, egg yolk, and vanilla extract. Mix well.
Add in the dry ingredients to the egg mixture and continue to mix.
In a mixing bowl, combine the flour, baking soda, salt, and cocoa powder.
In a separate bowl, combine the butter, granulated sugar, and brown sugar. Add in the egg, egg yolk and vanilla extract and mix. Combine with the dry mix.
Roll the chocolate chip batter and brownie batter into balls about 1 tbsp each. Then combine a brownie ball and a chocolate chip ball into one cookie shape so one half is a brownie and the other chocolate chip.
Place the cookie dough on a baking sheet and bake for 10 minutes at 375 degrees Fahrenheit.