1. Open up an empty canvas. I prefer mine to be around 500 x 500 pixels.

2. Using a hard brush with a width of about 50 to 80 pixels, draw a cross shape, like +. It doesn't have to be perfectly straight. You could always just use the shape tool and do it, but I prefer drawing it on.

3. Go to Filter >> Distort >> Twirl. You can drag the pointer thingy all the way to the left or all the way to the right. Rinse and repeat a second time in the same direction, or just click Ctrl + F.

And you're done! You may want to blur it slightly, because sometimes your swirl will turn out rather crunchy. Sometimes I rotate it or resize it to blur it, but that's just my way. You can distort it more by playing with other Photoshop filters, or twirl it the other way. It's all up to you. Have fun!