It does not get much more simple than this! It's called the Braid Roll and it's a great one to do on your own hair because it's so easy.
Begin with wet hair and pull it all back into a ponytail. Your ponytail can be high, low, or centered.
Now simply braid the entire ponytail VERY loosely. You do not want tight uniform plaits. I would just stick with a Regular 3-Strand Braid because you don't want to much clutter going on with this bun. Make sure to plait all the way down to the very bottom of the hair and then secure it with an elastic.
Now gently wrap the braid around that top elastic to begin and then around itself until all of the braid is up on the head. You can add bobby pins as you go along to secure it into place. It's not supposed to be a tight bun so remember to keep it loose.
Tuck your ends under the bun and secure it with a couple final bobby pins. It's elegant and simple and what could be better than that?