To make the seasoning, place the vinegar, sugar and salt in a saucepan, bring to a boil, reduce to a simmer and stir until the ingredients are dissolved.
Place the rice in a colander and wash thoroughly under cold running water. Leave the rice to soak in a saucepan with the 550ml of water for 30 minutes.
Bring the rice to the boil and then reduce to a low simmer. Cover with a lid and cook without stirring for 10 minutes. Remove from the heat and set aside, covered, for another 10 minutes.
Place the rice in a large bowl. Pour the vinegar seasoning over the rice and mix the seasoning through the rice. Continue turning the rice for a couple of minutes. Cover with a damp cloth and leave to cool to room temperature before serving.
Slice the tuna into thin strips, roll in the sansho and yuzu salt.
Wash the beansprouts and then trim the tops and bottoms from the chives.
Place half a sheet of seaweed onto a sushi mat. Spread the rice onto the nori leaving a 1cm edge at the top of the nori (this will be used to seal the maki). Smear on a little wasabi and then place strips of tuna, beansprouts and chives in the centre of the rice. Finish with a little sansho pepper.
Roll the maki using a silicon sushi mat. Slice into portions, cleaning the knife each time to avoid tearing the seaweed.
«Sear the tuna on a hot grill pan before using if you don't want to eat it raw.»