For the nuoc cham, whisk together all of the ingredients with 5 tbsp hot water in a small bowl. Set aside while you make the tempura.

Whisk the cornflour, plain flour, sesame seeds (if using) and a large pinch of salt together. Fill a large, deep pan no more than a third full with the vegetable oil and heat until it reaches 180C or a cube of bread dropped in browns in 20 seconds.

Quickly whisk the soda water into the flour mixture, being careful not to overmix, then dunk in the broccoli using tongs. Carefully lower into the hot oil and cook for 2-3 mins until crisp. Drain on kitchen paper, then serve with the nuoc cham on the side for dipping.