According to a judgement by a District Court in Ohio, it is best to do as my grandmother did and leave out an ingredient or two when you share your recipes because the courts aren't going to be of any help,  as reported by WIPR.  Apparently, the layout of a cook book itself may have originality such that it is protectable,  but not so much for a recipe itself.

Copyright protects works fixed in a tangible medium of expression that are original.  Copyright infringement ( or the violation of a copyright owned by another person or entity) may be proven by a "substantial similarity" between a work (e.g., book , music, computer software code, sculpture, ect.) and a work protected by copyright and access of the work alleged to be copied by the one alleged to be doing the copying.  This access can also be inferred by the same "substantial similarity" in certain situations.   

According to the Ohio court that issued the decision, a recipe is just a statement of facts with no creative expressive element (i.e., originality) and thus it is not protectable by copyright.

So do as my grandmother did, and leave a little something out when you share a recipe, if you really want to protect what is yours