Are flourless chocolate cakes leavened?

No. Yes. It depends. On what? On how how much you beat your eggs. If you want a denser and ultra-smooth custard consistency, you’ll scarcely want to beat them at all. However if you want a little more “cake-iness”, which I do since it’s called a “cake” after all, you’ll want to beat them quite a lot. I whip mine into a tall and ultra-light foam, which give the cake itself extra volume (from a slight mechanical leavening “push”), plus a very slightly crumbly crumb.