The original link is over on Pinterest (on my Pinterest page, it's under "Easter") but it's pretty easy to figure out. You need two solid eggs cut from felt and one felt egg with a 'window.
Decorate one of the solid eggs any way you like. I was careful only to glue the ends of the ribbon so the glue wouldn't show through.
Sandwich the decorated layer between the window and the solid layer, then sew all three together. I used embroidery floss and did it by hand, although a machine stitch would work nicely. Sew all around, leaving room to stuff. Then finish sewing and attach a ribbon to hang.