The first ten books can be seen here. The second ten are here. Nos. 21–55 are below this post.
56. Hervé Tullet, Press Here (2011) (10/21/16)
Tullet is known in France as "the prince of pre-school books." Here's a lovely video of him in "workshop" mode in a French preschool, learning from his small teachers just how his books really work.
I know a pair of twins who may enjoy this book in another year or so. In the meantime, I'll play with it myself. Sometimes, the simplest pleasures are the best.