Prepare the batter by mixing the ingredients together in a small mixing bowl. Refrigerate or place in the freezer to chill for 30 minutes.
Heat the oil in a heavy pot. When the oil is hot, remove the batter from the freezer, dip several pieces of yam in the batter and place in the hot oil. Don't place too many pieces in at a time as it will lower the oil temperature resulting in soggy tempura. Deep fry until crispy golden brown. Remove and drain on paper towels. Repeat until all yam has been deep fried.
Take a sushi mat, set it on the counter or cutting board. Place a sheet of sushi nori on the mat with the rough, dull side facing up. Take 1 to 1 1/4 cups of cooked sushi rice and spread it evenly on the bottom half of the sheet of nori. Moisten a wooden spoon or rice paddle and press down firmly on the rice to evenly spread and cover half the sheet of nori. Place several slices of tempura yam lengthwise across the bottom half of the rice. Pull the mat up with your thumbs, hold and tuck the fillings with all eight fingers. Roll forward in a jelly roll fashion, and tuck the nori forward, while pulling back the mat slightly each time you roll forward. Just before you reach the end of the sheet of nori, moisten the end with a little cold water. Continue rolling until you have a cylinder shaped roll. Tightly wrap the bamboo mat around the roll, and squeeze gently to seal the nori roll. Remove the mat and place the roll on the cutting board.
Moisten a sharp knife with water and cut the roll in half. Cut each half in half, then each quarter in half, moistening the knife lightly each time before cutting. You should now have eight equal size pieces of sushi. Repeat the above steps until you have 4 rolls of sushi. Sushi is usually dipped in shoyu before eating.
Yield: 32 pieces; 8 pieces per person
Per serving - 591 calories, 1 g fat (2% calories from fat), 11 g protein, 134 g carbohydrate, 5 g fiber, 0 mg cholesterol, 211 mg sodium