Is there a preferred way to go about this?
The app in question is not too large . . . single-player game that I wrote over the course of a couple of months.
EDIT: I should add that I have no experience with mac development . . . outside of what comes naturally with being an iOS developer.
EDIT: Classes heavily used in the game: subclasses of NSObject, UIView, and UIViewController. I don't know much about NSView, but I'm pretty sure all the UIView stuff will work in that class. Also some use of UITableViewController. I do also have Game Center, but I can leave that part out for now. There is no multi-touch.
EDIT: My graphics is all stuff that is in the QuartzCore and CoreGraphics frameworks. I do have a moderate view hierarchy.
EDIT: If you are doing such a port, you may also be interested in the issue of memory management
There's no easy way. It's that simple. Depressingly, you simply have to become good at programming the Mac.
"I'm pretty sure all the UIView stuff will work in that class" -- unfortunately, no. Everything is different that enough you have to work hard.
It's not a fun gig. Make sure you really, really think it's worth it financially.
Apart from anything else, be aware of the "sibling views don't work on OSX" problem if you stack up a lot of views in your iOS app. Essentially, you will have to change to using layers (instead of simply views) on the Mac if you rely on nested hierarchies of views here and there on the phone!
Click this link: Is there a proper way to handle overlapping NSView siblings? for the gory details on that particular problem!