I just tried out a sweet potato smoothie. I looked at a few recipes and then created my own simpler version with no sweetener.
1 small sweet potato, baked
1/8 tsp nutmeg
milk, to desired consistency

I scooped the sweet potato out of its skin, put all that in the blender. I re-heated it over low heat on the stove, but if I'd done it straight out of the oven instead of letting it cool, and added the cold milk, I might have had a drink of just the right temperature.

I'm eating it right now. It's very good. The sweet potato flavor is a little strong, but I don't think more nutmeg would help.