Microwave the potato until it's cooked. (Am I the only one who loves the existence of the potato button on the microwave?)
Cut the cooked potato into a few pieces and put it into the bowl of a stand mixer fitted with the paddle attachment.
Beat the potato until it's all mashed up.
Add a little powdered sugar at a time and mix until the mixture comes together like a dough.
Mix in the Nutella. Your candy is done now and you can make it any shape you want - the easiest choice would be to just roll it into balls. The instructions below explain how to make the shamrocks.
Grab a small ball of potato candy and press it into a shamrock lollipop mold.
Peel the shamrock out of the mold, break off any extra pieces, and press together any parts that may look off (the part you grabbed the shamrock from might be a bit out of shape).
Fill another lollipop mold with a layer of green sanding sugar.
Press the candy you just made into the mold with the sanding sugar and remove.
Repeat the process for the remaining candy. If the unmolded candy becomes too dry to work with, mix in a TINY drop of water.
Store in a sealed contained, separating layers of candy with wax paper.