Is it the one that's hovering near the bottom of the screen?
You can fall off a shelf then jump in mid-air to get back on!
Not this one. Litteraly in the shelve, in the middle of the platform after the ladder, you see the bottom of a cookie. The rest of the cookie is in the wooden shelve. You can see it by crouching on the shelve or by jumping from the shelve below. I got 100 cookie without this one, so I suppose it's just a bug.