1. To make tempura dipping sauce, combine sugar and water in a small saucepan and cokk over med heat, stirring, until sugar is dissolved. Add soy sauce and lemon juice, stir and set aside.
2. To make sesame topping, toast sesame seeds in a dry pan till golden. Crush lightly in a mortar and pestle while still warm, add soy sauce and sugar, then set aside.
3. Cut the chopsuey into 5cm lengths. Blanche in boiling water for 30 seconds, then shock in ice water, drain and squeeze out any excess water.
4. To make Tempura batter mix plain flour, baking soda and corn flour together in a mixing bowl. In a separate bowl crack the egg and beat it roughly, add cold water and mix gently. Pour the flour mix in batches into the egg mixture and combine gently.
5. Heat the oil to approximately 160℃.
6. Dust the blanched chopsuey with plain flour on both sides. Put into the tempura batter mix, then straight away into the oil. Only do a couple at a time so the temperature remains constant. Cook till lightly golden and crisp, turning once. Place cooked tempura on plate with paper towel to drain.
7. Arrange the tempura on a serving plate, top with crushed sesame and serve with a bowl of dipping sauce.