Develop stereo audio unit plugins

Develop stereo audio unit plugins

I want to develop audio unit plugins(for example, stereo panner) with
stereo inputs and outputs. (This app don't have the relation to iOS app.
I'm talking about audio unit plugin for any DAW(Logic etc).)
The following code is very simple audio unit plugin code.
https://developer.apple.com/library/mac/samplecode/StarterAUEffectWithCocoaUI/Introduction/Intro.html#//apple_ref/doc/uid/DTS40011650
But, this code is for mono plugin. How do I write code to extend stereo
mode or where web pages should do I look up for sample code and so on.