How to use data-options@: to select options from another content type

I want one content type, say ‘Book-titles’, to have a field ‘written-by’ that is populated from a different content type, ‘Authors’. Thus the editor can only choose an author that has already been listed in the system. (To avoid duplications, spelling inconsistencies, etc.)

I asked this question back on Feb 27 and was advised to use data-options@ or possibly @data-options with '\Grav\Common\Page\Pages::getTypes' but what I got was a lis of blueprints, not an array of options.

I don’t understand this part of Grav and my experimentation has been fruitless. Can anyone give me a solution?