Slice the ends off a cucumber and cut it to the same length as the nori sheets (about 20cm). Cut the cucumber into quarters lengthwise and remove the seeds carefully with a spoon or a knife. Cut the sticks lengthwise into half again, so that you have 8 sticks of cucumber. You will need 4 sticks for this recipe, so wrap and store the rest in the fridge for 1-2 days to use in other sushi.

You will be able to see some thin lines on the nori sheets. Following one of these lines, cut each sheet in half with scissors, but be very careful as the sheets break easily. Add a half-sheet of nori, shiny-side down, on the bottom half of the sushi mat, with the lines of the sheet lying horizontally across the mat.

Wet your fingers in the bowl of water and shake off any excess. Damp fingers help when handling sticky sushi rice. Look for a line in the nori sheet about 1cm from the top. Keeping the top 1cm of the sheet clear, spread roughly 80g rice over the sheet evenly and gently press with your fingertips. It must be a very thin layer of rice (about the thickness of a grain of rice). Put the cucumber stick in the centre of the rice, then you can add some wasabi to the centre before you add the cucumber, if you like.

To roll the sushi, hold the filling in place with your index fingers, start rolling with the mat from the bottom edge of the nori towards the top of the rice edge. Make sure both the rice and filling are holding their place tightly. Open the mat; you should be able to see the 1cm piece of nori that does not have rice on it. Finish rolling.

To cut the rolls, remove the sushi from the mat and set on a clean, dry chopping board. Gently cut each roll into six pieces (or eight, if you would prefer very small pieces) with a sharp, wet knife. When you cut the sushi, slice it very smoothly and quickly. I recommend cleaning the knife after every cut. Repeat with the remaining nori sheet and filling ingredients. Put the cucumber rolls on a plate and sprinkle with the toasted sesame seeds.