Prawn Tempura Rolls

Name: Prawn Tempura Rolls
Prep time: 55 min
Cook time: 2 h 40 min
Total time: 3 h 35 min
Cuisine: Asian, Japanese
Ingredients: 20 large raw prawns, peeled; 1000 g water, plus extra for brushing; 250 g sushi rice, rinsed well; 2 Tbsp rice vinegar, plus 2 Tbsp for brushing; 1 tsp sugar; 1 tsp fine sea salt; 3 tsp sriracha sauce; 3 Tbsp mayonnaise (kewpie); sunflower oil, for frying; 140 g plain flour; 1 Tbsp cornflour; 260 g sparkling mineral water; 4 sheets nori seaweed; 2 Tbsp toasted sesame seeds; 2 fresh jalapeño chillies, cut in matchsticks; ¼ cucumber, cut in matchsticks, deseeded; ½ avocado, thinly sliced (2 mm); soy sauce, for dipping