https://tiffinandteaofficial.com/milk-buns/#wprm-recipe-container-11769
This is the one I used. I had to look on other versions to find out what state the butter needed to be in as it doesn't say, but it needs to be melted (which is what I'd assumed but I wanted to be sure). Other recipes skip the tangzhoug stage (but it's so easy I don't see the reason to), or use powdered milk (not helpful when you have liquid milk to use up). So I stuck with the first recipe I'd found.
My DD got up this morning and asked if there were any yummy buns left, or had I eaten them all.

Good thing I had another batch in the oven.
I'm going to try them in a square tin next time as covering them for their second rise is too tricky on a flat baking sheet as they want to stick to whatever you cover them with. I also tried just egg yolk with a splash of milk for the egg wash and I think they are more shiny than when I used the whole egg.