For the miso-marinated salmon: heat the miso, sake and mirin in a heavy-based saucepan until just heated through. Tip into a bowl and allow to cool.
Smother the salmon steaks with the marinade, put them into sealable food-grade plastic bags and leave to marinate in the fridge for 2 days – you can move the salmon around in the bags to ensure it is marinating evenly from time to time.
For the rice: wash the rice really well in a sieve set over a large bowl, changing the water at least three times. Drain well.
Put the washed rice into a large heavy-based pan with a tight-fitting lid. Pour over 400ml of water and leave to stand for at least 20 minutes (up to 30 minutes is fine).
Dissolve the sugar and salt in a small pan with the rice vinegar over a medium heat. Allow to cool to room temperature.
While the sugar and salt are dissolving, bring the rice to a boil and then reduce to a low simmer for 15 minutes. Do not remove the lid, but leave to stand for a further 15 minutes.
Tip the rice onto a large flat clean tray - a cold metallic one is best as it will help the rice cool down quicker. Drizzle over half of the cooled vinegar mixture.
Using a spatula or a large metal spoon, fold the rice very carefully so as not to break up the grains. The rice will absorb the vinegar and become glossy. Add a little more of the vinegar mixture and keep folding until it is absorbed - you do not want the rice to be wet, so add the last little bit of vinegar sparingly and don’t worry if there is a little left over. Leave to cool (fanning helps the rice to cool quicker - you can do this with a magazine or newspaper).
For the dressing: place the mint and coriander in a food processor, along with the garlic, ginger, light soy sauce (or Thai fish sauce), wasabi and lime juice. Blend until all the ingredients are puréed; then slowly drizzle in the sunflower oil through the feeder tube to make a glossy emulsion. Transfer to a screw-top jar and put in the fridge until required.
. When you are ready to cook the salmon, preheat the oven to 180C/gas 4 and wipe off any excess - but not all of - the marinade.
. Heat a frying pan over a medium flame, add the salmon (skin-side down) and fry for 2-3 minutes.
. Transfer the salmon, again skin-side down, to a baking tray and roast in the oven for 6-8 minutes, until just cooked through. You can baste (spoon over) more of the marinade during cooking to keep the fish moist.
. For the salad: carefully fold the dressing into the rice and then fold in the cucumber, spring onions, chilli and pickled ginger.
. Serve the miso-marinated salmon with the sushi rice salad at once.