Page 43 - Peter Randall "The Craft of the Knot.."

Butterfly Loop (see Chapter 3), and can even be tied the same way if the
ends are attached.

STEP 1 Place two ropes side by side—one on the right and one on the
left—and cross the running ends, forming loops.

STEP 2 Use the right-side cord’s running end to make a second loop.

STEP 3 Use the left-side cord’s running end to make its second loop as
well.

STEP 4 Tighten down the knot by pulling apart the two standing parts

and tugging down the running ends.