Make the Dough: Cook the potatoes until tender and remove the skins. While your potatoes are still hot, rice or mash them as finely as possible into the butter and salt.
¾ lb Russet Potatoes, ¼ tsp Himalayan salt, 1 tbsp salted butter
Add the potato starch and water to the potatoes and work it into a dough for a minute. The dough should be soft but not sticky and will have the texture of firm mashed potatoes. *Note, this is not a stretchy dough. Once you fry them the texture will change to being like mochi.
3 tbsp potato starch, 3-4 tbsp water
Rest and Shape: Cover and let the dough rest for 10 minutes then divide it into 12 equally portioned balls. Roll each ball until smooth and then gently press down on them to form a disc (see note). If the balls crack or split around the edges from being too dry, moisten your fingertips and gently run it over the cracks to seal them.
Chill: Set your shaped potato mochi in the fridge for 10 minutes.
Make the Sauce: While your mochi chills, make your sauce by gently heating the soy sauce, sugar and rice vinegar until the sugar has dissolved and the sauce begins to thicken. (you can do this either on the stovetop in a small saucepan or in the microwave in short 15-20 second blasts, stirring between each round (just be careful when removing the bowl to stir as it will be hot).
2 tbsp tamari, 3-4 tbsp raw cane sugar, 1 tbsp rice vinegar
Fry your Mochi: In a pan or skillet, add enough oil to shallow fry your potato mochi and bring the oil up to about 325°F-350°F. Add the mochi to the pan, ensuring that they don't touch each other.
Oil for Frying
Fry until both sides are golden brown. (about 2-3 min each side). If your mochi is on the thicker side and you have a white ring in the middle after your fry both sides, you can stand them on the edge to allow them to brown.
Cool and Sauce: Remove your mochi to a paper towel-lined plate to cool a bit and then brush both sides of your mochi with the sauce or dip each one into the sauce and allow the excess to drip off. Enjoy immediately (see notes).