Custom widget with designer

[Josef Lintz]

I want to create a widget which will be shared among applications.
I'm following this tutorial, which so far explains most of what I need. However, my widget is slightly more complicated than just a single button.
I want to be able to "design" my widget if necessary. I know that you can edit the qml in *Plugin::domXml() function, but this is very time consuming, and tedious.
According to this you can use a ui tag in *Plugin::domXml(), to reference a *.ui file. But I don't really understand how to do it.

Any help is greatly appreciated.