Sex.

Serious answer: In the past I’ve made apple sauce/compote, reheated meals, boiled eggs, steamed vegetables and dimsum, reheated/cooked stuff like soup, etc. etc.

Also useful as a bain marie. Apparently you can also make bread and cakes in them. Also hot chocolate.

Honestly, if I ever move to an appartment, I think a rice cooker, air fryer, and microwave would allow me to do almost all of my cooking.