Search Across Notebooks

I am in the process of breaking up my small number of notebooks into a larger set of notebooks, for performance reasons. The problem I am starting to discover now is a difficulty in finding notes. I know a note exists - but I am now not sue in which of my notebooks it is. What would be great is to have an option in CN to search across all notebooks (all the ones listed in the File menu, so only the open ones).

At the moment, in this case, I simple have to open each notebook one at a time, and do a search on each one until I find the note I want. It's do-able, but not ideal.