I'm trying to set up a chapter heading which looks like this:

Chapter 4

This is the fourth chapter

That is, there are two lines, one of which says "Chapter" followed by its number, and the next which is the chapter title. What is the easiest way to do this? I've tried

\def\chap#1#2{Chapter #1\crlf #2}

\setuphead[chapter][
       command=\chap,
       style=bfc,
       after={\blank[1cm]},
    ]

But this doesn't work (and nor do many other variations in the "chap" command). I'm a bit stymied here - and I'd welcome some advice.

Thanks,
Alasdair