Hi, I'm Mike Patrick, and this is How to do a Cascade, a shuffle flourish. You take the cards, you shuffle them, and you allow them to simply cascade into your other hand. The method is that you must do a pharaoh shuffle. The better your shuffle is, the more smooth the cascade will fall. If you have big gaps in between it won't look so good, so this is why you wouldn't do it with a riffle shuffle. You need a lot of precision. So you do a pharaoh shuffle and you put them into an upside down "v". It looks like a "v" from my perspective, but you do it like this. You'll have to experiment with your hand size exactly where you want the cards to be positioned.
You go into this like you're going and you place your thumb in between here, and I can hold this like this indefinitely. When you're ready to do the cascade, your pinky is here, your index finger is here, your thumb is on top, you place your other hand underneath, and you simply let go with your thumb. The cards will fall naturally in this position, and you'll have to deal with the fear of them falling all over the place a few times. Once you get past that to just let go and they will fall straight into a cascade.
I often don't even bother using my thumb. What I do is I just shuffle them, position them, get these cards in a position I just let this hand drop right in front and it starts immediately. It's a very, very impressive way to end your shuffle. That's how you do a cascade.