Had the opportunity to spend a week training with Professor Trey Howard from Gracie United Slidell. He taught this choke from the turtle position that will definitely be a part of my arsenal.
I learned this choke several years back but with a thumb in grip on the back of the neck instead of the fingers in. Once it is in I've worked on actually dropping in to a marcelotine style finish where you drop under the uke with a shin across the waist, hooking with your instep and throwing the free leg over the back. Not sure if this makes sense in writing but it has worked well for me.