WOW! That's really all I can say about this.
The amount of cognac that I used was about three shots worth. I also used three vanilla beans split down the middle and cut into one inch pieces. They sat in the cognac for about a week before adding the whole thing to the brew. I then let it sit another week before kegging it. It came out way better than expected. The stout is amazing on its own, but even better with the hint of the cognac and vanilla in the back. Will be doing this one again!