For the Brownie: Preheat oven to 350 degrees F. Grease a 9x13 pan. In a large mixing bowl, mix sugar and cocoa powder together. Mix in the melted butter, eggs, and vanilla until smooth. Add the flour and salt and mix until just combined. Spread into the greased pan.
For the Cookie: Cream the butter and sugars together for 2 minutes and then mix in the egg, egg yolk, and vanilla. Add the dry ingredients and mix until combined. Use a wooden spoon to mix in chocolate chips. Scoop out spoonfuls of dough, flatten with your hands and piece together over the brownie batter (or you can put all the dough between two layers of plastic wrap, roll out, and then place over batter). Sprinkle more chocolate chips on top if desired. Bake for 35-40 minutes or until cookie is golden, tenting with foil if the top is getting too brown. Let the brookies cool completely before cutting.