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; 250 g sushi rice; 1 tsp sugar; 1 tsp fine sea salt; 2 Tbsp rice vinegar; 3 tsp sriracha sauce; 3 Tbsp mayonnaise; sunflower oil; 1 Tbsp cornflour; 140 g plain flour; 260 g sparkling mineral water; 4 sheets nori seaweed; 2 Tbsp toasted sesame seeds; 2 fresh jalapeño chillies; ¼ cucumber; ½ avocado; soy sauce