Peel the sweet potato and slice into rounds. Put them in a pot with enough water to cover, and boil. Once a skewer goes through the sweet potatoes easily, drain well.
Put the sweet potato in a bowl, mash with a rolling pin, and pass through a strainer. The texture will become smooth by straining the mashed potato (straining is optional).
Add the ★ butter, sugar, egg yolk, and heavy cream to the mashed potato, in that order, mixing well after each addition.
Cut off a corner of the bottom of a plastic bag, and fill with the Step 3 mixture. Pipe the mixture into small baking cups and bake in a toaster oven, making sure not to brown them too much.
Story Behind this Recipe
Potatoes are now in season, so I bought sweet potatoes. My hubby was excited and made these. We didn't have a piping bag, so he used a plastic bag instead. The end product turned out to be surprisingly unique looking, so we were thrilled.
It's better to use soft butter. We used the "Naruto Kintoki' variety of sweet potatoes. Adjust the amount of sugar depending on the variety of sweet potato you use . If you prefer, use egg yolk for an egg wash.