Get in the free position, reach your back hand further back on the boom, and head down wind while sheeting in the sail. You can slightly lay down the sail for an easier duck.
Let the board settle into a nice deep carve, just past a broad reach or a little further. Initiate the maneuver by releasing the front hand and pull the clew hand up toward your head.
Reach the open hand to the clew end of the boom by crossing your arms while keeping your knees bent and carving the board.
Now yank your new clew hand across your body and out away past your leeward ear. Yank quickly and aggressively because the pull is important so the boom will rotate to a position for you to reach the other side properly.
Reach the new forward hand to the front part of the boom. The mast edge of the sail may want to fall toward the water. No problem -- as long as it does not touch the water. If it does, you are going for a nasty crash over the nose of the board.
Grab the boom on the windward side of the sail. Remember to keep carving the board by bending your knees and leaning forward. If you have tons of speed then you can really slash out of this turn otherwise perform a wider arc with less rail pressure to keep the board planning out of the maneuver.
Switch the feet, trim, adjust, and sail away.