The recipe for cornstarch goop is super easy. Simply mix equal parts cornstarch and water with your hands. Here we have photos of Emelia playing with it, and a little video we did to demonstrate how strange yet fun it is!
I don't recommend saving it for more than a day or two though. I tried saving it for a week thinking it might just dry up but when I opened the tupperware that I stored it in, it smelled worse than a dirty diaper.