The obvious guess is that it's for cooking either
a whole chicken or some eggs.

http://cgi.ebay.com/_W0QQitemZ130110245902

But there are only four holes in the ceramic
plate that fits in the bottom, and the holes
are too small for eggs.

I'd guess it's for steaming a whole chicken,
but who wants steamed chicken? Seems like
it'd be an awful mess, and not for anything
particularly good. It might be a useful
appliance for somebody who did not have
an oven.