The New York bookseller McNally Jackson here posts a fascinating list of its bestselling titles of 2011, but there’s one big surprise: the bestselling thing in the store isn’t a book from a publisher large or small, nor is it a book at all: it’s the set-up fee the store charges customers who want to self-publish a book on McNally’s Espresso Book Machine.

What’s more, the store seems to be selling a lot of books on its Espresso machine. Coming in at number 18 on the list is the sale of  “All the public domain books from the Espresso Book Machine,” which includes titles from Ingram and Google Books.

If this New York Times story from October is to be believed, McNally Jackson is selling “almost 700 self-published works a month.” Add to that a healthy number of public domain titles, and it’s possible that McNally Jackson is eeking out a profit on its Espresso, which costs about $100,000 or can be leased (according to this Boston Globe piece) for about $1,500 a month.

The costs of McNally’s self-publishing business are detailed on the store’s site: “One-Time Self-Publishing Set-Up” is $15; “Standard Self-Publishing Set-Up” is $99 and includes, among other things, staff help and the opportunity to sell your book at McNally Jackson itself.