Some memory help please

[Harry Putnam]

I know I can show the summary buffer sorted by date.

But if the view is threaded then "By date" may still not list messages
by date.

I remember a command I used many times to unthread the buffer and
display the messages by date... but it his sank into the swamp of my
memory, and having a heck of a time digging up the proper commands
with emacs help searching.

Can someone tell me how to make what is usually (in my setup) a
threaded summary buffer, unthreaded and sorted by date?