How to effectively start developing a widget application for OSX?

Question

macOS

Hello,
I wrote a bunch of scripts and notifications for one of my most popular activities. But I'm starting to understand that writing a simple widget for OSX will be much more efficient.
Perhaps someone had experience? I googled something and did not find anything that is directly very useful. Any resources to get started? Examples with code? Preferably such resources that can be used as a reference, and not those where you have to read the whole book to understand what to do.