When creating Custom Renderer how to call native method from PCL?

Easy for you gurus...

I'm creating a custom renderer for Maps.
Now I'd like to create an additional custom method (e.g. updateMarkers) on the PCL class that extends Maps.
How do I implement that method on the native layer? Do I need to create a Dependency Service?

Bear with me, I'm doing this for the first time...

Thanks!