Not a rock, but any cast iron pan works well!

Want something REALLY handy? Get yourself a cast iron mini cocotte!

Le Creuset:

https://www.lecreuset.com/cast-iron-mini-cocotte/21001US.html

Staub:

https://www.zwilling.com/us/staub-cast-iron---minis-0.275-qt-mini-round-cocotte-grenadine-1101087/40509-805-0.html?cgid=our-brands_staub_cast-iron_minis

Lodge:

https://www.houzz.com/products/lodge-black-enameled-cast-iron-mini-round-cocotte-set-of-2-prvw-vr~130298261