When I close my MacBook - my Ultrafine 4K display stays on (I want everything to sleep) When I close my MacBook - my Ultrafine 4K display stays on (I want everything to sleep). It's connected via USB-C.

I can find nothing about this on Google - in fact I found articles telling people what to do to make an external display stay on (like it goes off by default).

Mine stays on by default - when I have stopped using the MacBook and want to step away from my machine - I just want to close it, have the machine sleep &amp; monitor go off and be done. How can I do this?
This is normal closed clamshell mode for the MacBook so you would need to script a sleep event or to sleep your display:

Control–Shift–Power button or 
Control–Shift–Media Eject - https://support.apple.com/en-us/HT201236

You can make use of normal lock timeouts for screen sleeping, power savings and locking. 

If you had no keyboard or input devices connected, it should sleep automatically once the system detects you can’t type or mouse with the lid shut.