This is a recipe for smooth purple sweet potato treats that don't use eggs or heavy cream. Simply steam sweet potatoes until soft in a pressure cooker or rice cooker, then mash them while still hot and mix with butter, milk, and sugar to create a moist and delicious dough. Using a piping bag will give you beautifully presented treats. Combine it with butter cookies you have at home to easily enjoy an Okinawan purple sweet potato tart-style dessert. After chilling in the refrigerator to set the shape, bake it in the oven to add a crispy texture, making it a perfect treat for your home cafe or for entertaining guests.