This was the 'Lever Card' I posted sometime last month--you can see the posting HERE.
I found a lever-card tutorial at Splitcoaststamperdone by Laura Lipe--you can view itHERE. Laura's card size is 4¼" x 5½" (when the card is folded)--that's known as an A2 card size. My preferred card size, as you may know, is 6" x 6", so I've revised the measurements to those for that card size.
As requested, here's the template for a 6" x 6" (15cm x 15cm) Lever Card: