How can I purée my sweet potato casserole without a food processor?

fork will work or potato masher if you have more than a fork will handle
recommend The Unplugged Kitchen by Viana LaPlace so you have a reference for these occasions of mechanical dysfunction

yeah, i'd try a mixer or blender. honestly, our sweet potatoes called for being whipped in a food processor, but i just mashed them by hand a lot. I think they turned out fine without the extra whipping.

A blender, stand mixer, or even a potato masher or ricer could work, depending on what you've got! Sweet potatoes are pretty flexible like that.