Peel 250 g daikon radish and cut it into thick half moons. Place them in a pot of cold water, bring to a boil over a medium and then lower the heat. Simmer until fork tender, top up the water if needed. Once cooked, drain in a colander.
Cut 250 g yellowtail fillets into rough chunks and place them in a heatproof bowl. Sprinkle with ¼ tsp salt.
Prepare a bowl of ice-cold water, then pour freshly boiled water over the yellowtail.
After 10 seconds, transfer the yellowtail to the cold water. Drain the water and pat each piece dry with kitchen paper.
Place the yellowtail and daikon pieces in a clean pot and add 120 ml water, 60 ml sake, and 1 tbsp light brown sugar. Heat on medium and gently mix until the sugar dissolves.
When the liquid starts to boil, reduce the heat to medium-low and add 1 ½ tbsp Japanese soy sauce (koikuchi shoyu), 1 tbsp mirin, 1 dried red chili pepper and 5 g dried kelp (kombu).
Place a drop lid (or foil/baking paper cut to size) on top of the liquid and simmer gently for 15 minutes. While you wait, peel 10 g ginger root and cut it into fine matchsticks (these will be used to garnish).
Remove the drop lid and kombu. Increase the heat to high and boil for 2 minutes.
Divide the yellowtail and daikon between serving bowls and add a small amount of the cooking liquid. Garnish with ginger and enjoy!