This was literally a ten minute project. I'm sure that there are tons of little things you could do to fancy it up, but I didn't want fancy this time.
This is the shirt I used. It's a 12m, and a little too scruffy to sell back to the baby stuff store. I started by cutting out my shape-
Even out the edges, then sew the sides and bottom of the shirt together so the only opening is the neckline.
If you look carefully, you'll see that I also sewed across the corners. I wasn't happy with how this step came out, so I'm skipping it for the tute.