Prepare Potatoes: Peel and cut starchy potatoes into chunks, boil until fork-tender, drain and mash until smooth.

Make Mochi Dough: Combine mashed potatoes, glutinous rice flour, and sugar in a bowl. Gradually add water while kneading into a smooth dough.

Shape Rolls: Divide the dough, flatten each into a disk shape, and roll into cylindrical shapes.

Fry Rolls: Heat oil in a skillet, fry shaped rolls until golden brown on each side, about 3-4 minutes.

Serve: Remove rolls from skillet, drizzle with soy sauce, and optionally sprinkle with sesame seeds and green onions.