Peel sweet potatoes and put them in a bowl of water after each one is peeled so they won't turn black. Slice them lengthwise ?" thick and return to water. Be careful not to cut yourself because the potatoes are kind of hard. Heat oil in a deep fryer or a deep skillet to 375?. Take enough potatoes out of the water to make a batch without crowding and pat dry. Drop in hot oil and fry for 3 minutes or until tender all the way through. Drain on paper towels and sprinkle with granulated sugar.