One of my favorites to use for all sorts things that require a loop that does not slip but is easy to undo. The alpine butterfly is one of the most attractive knots too. Thanks to Albert Hinton who reminded me that you can always relearn much easier ways of doing stuff.

Step1:
wind the rope around your hand crossing the first time

Step 2:
Wind a second turn alongside the first.

Step 3:
Grab the middle piece of rope (helpfully coloured purple here for you):

Step 4:
twist it under the left hand side of the bundle and pull through

Step 5:
Slide the rope off your hand and gently tighten the ends and loop.