A one handed break that I made-up when I was in Junior High School. It could be the "official" way to do it, or it could be really poor form. I wanted to do a one handed cut, and there was no Internet to search back then, so I had to figure it out for myself.
Take all the cards in one hand. Hold them with your four fingers (assuming you have four) along the back of the deck, and your thumb on the other side. You want to just bearly get the tip of your fingers over the top of the deck.