Well wouldn't you know that I didn't have any large square envelopes, so I had to make one! I scored a 12" x 12" piece of Vanilla cardstock in at 2 3/4" on each side. Cut the corners off and stamp it.
Then I made a flap to cover the gap where the cardstock doesn't quite meet. Flap is 6 1/2"ish x 2 1/2". Stick that to the top flap only. Close shut with ribbon!