Wash the rice thoroughly and allow it to soak in the cooking water for 30 minutes. Place rice, salt and water in a saucepan with a fitting lid. Cover and bring to the boil. Reduce heat and simmer gently for 45 minutes until all water has been absorbed. Remove from heat and let stand for 5 minutes, covered. In a small saucepan gently heat vinegar and mirin. Do not burn.
To remove rice from pot, insert a wooden paddle or spoon between the rice and the wall of the pot and run it around the circumference. Place all the rice in a low walled container (if possible) to prevent mashing the grains. Without disturbing the rice, allow the vinegar-mirin mixture to run along and off the rice paddle, pouring it on in a circular motion. After 10 seconds, with vertical cutting movements of the paddle, mix thoroughly. The liquid should be completely combined with the rice in about 1 minute. While mixing, fan with a hand held fan to drive off the steam (this firms the surface of the grain and gives a slight gloss). If no hand held fan then use a firm piece cardboard to fan rice. When finished, cover with a damp cloth, making sure it does not touch the rice.
Note: soak brown rice overnight before cooking, especially if it is not pressure cooked. This allows the rice to become sticky so when rolling it will stay together. If there are problems with the sticky consistency of the brown rice, substitute 1/4 of the total volume with sticky white rice (glutinous rice). This is available at health food stores. If traditional soy sauce (tamari or shoyu) is used to dip nori in at the table, then less salt should be used when cooking rice.
Place a bamboo rolling mat on a flat surface. Prepare a bowl of vinegared water (1 part vinegar to 2 parts water) for rinsing hands. Place a sheet of nori vertically on the mat. The outer side of the nori should be down. Take a little wasabi paste and spread onto the top of the nori sheet closest to you, lengthways. Spread the rice evenly over the sheet of nori, leaving 3-4cm at the far edge of the sheet uncovered. At the edge closest to yourself make a groove in the rice and lay the filling along the rice.
Filling examples: tempeh, carrots, cucumber, avocado, pickles. Any type of filling may be used.
Picking up the corners of the edge of the rolling mat closest to you, roll the nori and filling away from you until the front edge reaches the rear. Without removing the mat, lightly pat the ends of the roll and firm them. Lightly moisten the nori and this will stick the nori together. Remove the mat and cut. Make sure that the knife is sharp and moist before cutting.