To recreate Katy's look:
1. Divide the hair into two sections (front and back) by running the tip of a tailcomb from ear to ear.
2. Pull the front section back off the face as if creating a ponytail and then twist the hair until it twists back on itself to form a coil. Tuck the ends under and use pins to hold the twist in place.
3. Scoop the back section of hair up into a high ponytail and secure with a hairband right at the base of the top-knot twist.
For a super-sleek take on this look, straighten the hair before styling; for voluminous waves like Katy's, use tongs on the ponytail for extra body.
If your hair is fine or too short, scoop into a ponytail and use clip-on hair extensions to create the twist.