First make your sushi vinegar - you can buy this ready-made, but it is easy to make your own. Warm the vinegar in a pan, then add the sugar and salt and let it dissolve. Leave to cool and you have the wonderful sweet savoury dressing for the rice. Set aside.
Wash the rice three times, then drain and leave to stand for 15 minutes. Bring one litre/1¾ pints of cold water to the boil and add the kombu (if using) and the rice. Simmer with the lid on for ten minutes, then leave to stand without taking the lid off for another 20 minutes.
Tip into a large wooden bowl, sprinkle on the sushi vinegar and cut through into the rice with a slicing motion with a wooden spatula.
Fan to cool, with a wooden paddle (or an old tablemat), for ten minutes. Turn the rice over, fan for two minutes. Repeat this four times and the rice should be at room temperature and just sticky enough.
Use the rice immediately as it is past its best after a few hours.
For the nigiri sushi, cut your chosen fish carefully into strips. Always try to get sushi-grade fish, and always use top-notch fresh fish - some sushi fish has been deliberately frozen to kill any bacteria.
Take the prawns, peel them leaving the tails intact and butterfly them carefully taking the dark strip out from underneath. Impale them on a skewer lengthways to take out the bend.
Place 500ml/18fl oz water in a pan with the sake and bring to the boil. Simmer the prawns until pink - this should take about two minutes. Leave to cool and remove the skewer. You will have straight prawns which will be easy to place on the rice.
Take a ball of rice about the size of a walnut, roll it in your hands to polish the outside, but don’t compress the rice too much.
Place a dot of wasabi on the top. Place a prawn or a fish strip onto this. Press into place with a tapping motion between your thumb and middle finger. Repeat to use up as much of the fish as you wish to turn into nigiri.
For the maki rolls, take a bamboo-rolling mat, cover it liberally with cling film. Take a half sheet of nori seaweed. (The ones made with half a sheet are smaller and have more filling to the rice ratio, and are a better eat.)
Cover with rice all over except for the edge facing you, where you need to leave an empty border of about 2cm/¾in. - this will give you a join. Press the rice down firmly but gently to give you a thin but even coating. Down the middle, line up your strips of filling – choose from salmon, cucumber, avocado and wasabi. Roll the mat away from you, catching the filling into the roll. Firm up with the mat.
Unroll and using a knife with a damp blade cut into bite-sized pieces.
Serve the nigiri and maki rolls with pickled ginger, wasabi and soy sauce.