Boil the sweet potatoes in plenty of water with 1 teaspoon of salt.  When cooked, mash them until smooth.  Keep aside to cool them.  Mix the rice flour with the water, ½ teaspoon of salt until you have a smooth batter.
When you are ready to fry the fritters, divide the mashed sweet potatoes into as many portions as you want.  Take a portion and press it flat on a plate or on the palm of your hand.  Put ½ teaspoonful of sugar or cheese on to the portion of sweet potato, close the potato round this filling, and form the fritter into a ball or the shape of a croquette (sugar is better for a breakfast fritter, while cheese makes it a more savory dish).  Repeat the process until all the ingredients are used up.  Dip each fritter into the rice-flour batter before frying them in several batches until golden brown.  Serve hot, warm, or cold.