Just like other double line knots, this is just a variation of its name sake with your line doubled before beginning to tie the knot.
Start just like a regular Jam knot, except double your line first. We usually pinch the line where we double it leaving several inches of tag and doubled line to work with on these knots.
1. Double the line and pass it through the eyelet, allowing yourself several inches of doubled line on either side of the knot.
2. Run the doubled tag parallel to the doubled mainline section and pinch it together about an inch or two above the eyelet.
3. Begin wrapping around down the 4 lines 5-7 times.
4. When you get to the bottom pass the doubled line between the two doubled lines at the bottom (should be an opening there).
5. Bring the tag end up through to loop created when you started wrapping down.
6. Moisten the lines and pull the loop, tag and mainline all together to tighten the knot.
You can pull the loop to tighten the wraps and pull the tag and mainline together to tighten the knot against the eyelet. Again it’s a lot of line to manage. The key is learning how to the pinch the lines together and hold them with two fingers while you wrap with other fingers. If a lure weighs enough you will see some anglers swing the wraps around the lure in a circle fashion.