It looks like an egg in an egg.
One of my poor pullets laid one too. But the outer egg didn't quite close the tip of the shell. And the inner egg didn't have a shell at all.
Open up the smaller egg and it will likely have the yolk and some albumen.
The outer egg of the one my pullet laid had funky looking albumen and I ended up popping the inner egg while I was examining it, but the inner egg looked fine other than lacking a hard shell.