On the WP Recipe Maker > Settings > Recipe Collections page you can restrict access to this feature to logged in users only and set a message to show to regular visitors instead:
We use the default WordPress user system for this. Because of that you can use any of the numerous front-end login and registration plugins out there in combination with WP Recipe Maker.
Another option is to use a membership plugin that allows you to restrict access to the page with the Recipe Collections feature on it. This allows you to provide the feature only to paying customers, for example.