A simple set of a front piece with a window and a flat back (both with a hole for hanging). Laser cut from medium-weight chipboard.
Plus an extra piece that extends about 1/8" around all sides. You could turn this into 2 ornaments or one that is double-sided (if you use the larger piece sandwiched between the other 2, you'll have a bigger bauble showing outside the front-most pieces on both sides).
Bonus: see the extras photos for 2 tips: Even the largest layer is sized so you can cover it with a sheet of paper from a 6x6 paper pad (the Vintage Christmas 6x6 Paper Pad is shown in this example). AND: the window cut in the front chipboard layer also fits the Clear Plastic Round Domes (in case you want to turn the ornament into a shaker card). Clear Plastic Round Domes sold separately.
Teri Calia made a Christmas Ornament (see the wide photo below). More info in the blog and/or see the supply list.