Its that time of year here in the US of A that sweet potatoes are on sale, so I thought about making a beer with them. I found this https://youtu.be/rwcEllQZpLE
Yes. You can mash (as in enzymatically convert starches to sugars, not as in mashed-potatoes) any gourd (think pumpkin, squash, potatoes, sweet potatoes). They tend not to add too much noticeable flavor to a beer (just a general earthiness and some color contribution) so it's often recommended to oven roast them a little first to get some caramelization. Here is a recipe that uses sweet potatoes.
I sometimes use sweet potato for beer in a similar way as I do pumpkin. Just clean it up, shove it in the oven until it caramelizes a bit, mash it with a fork or whatever is at hand and add it to the mash - I usually use 1-2 kg (~2-4 lbs) for a 20L (5 gal?) batch. And from then on it's brewing as usual. Gives a nice colour to the beer though I can't say I've noticed any flavour.
Read about being able to mash them on their own, but I've yet to try that, not sure how I would go about it.