Combine mirin, sake, and sugar in a pan and boil to dissolve sugar.
Add miso paste, bring to a boil, and simmer for three minutes.
Strain the mixture through a fine sieve and let it cool.
Coat salmon with marinade, reserving some for later, and marinade for six hours.
Preheat the oven to its highest setting.
Wipe excess marinade off salmon and heat a dry pan until very hot.
Sear fillets briefly in the hot pan then move to a baking tray.
Rub reserved marinade on top of the salmon and dry for 10 minutes.
Bake in the oven for five minutes until just cooked.
Mix cucumber, chilli, and mushrooms with salt for the salad.
Rest vegetables for 30 minutes, then rinse and pat dry.
Boil vinegar and sugar, pour over vegetables, rest for one hour, then add ginger.
Drain pickling liquid before serving.
Boil rice vinegar, sugar, and salt together then let cool.
Wash sushi rice and drain in a colander for 30 minutes.
Add rice and 500ml water to a pot and bring to a boil covered.
Simmer for 15 minutes, remove from heat, and rest covered for 15 minutes.
Tip rice into a bowl and fold in 4 tablespoons of the vinegar mixture.
Shape cooled rice into balls or triangles and warm before serving.
Garnish salmon with sesame seeds, cress, and seven spice pepper to serve.