Rinse the rice well. Put the rinsed rice, sake and konbu seaweed in the bowl of a rice cooker, add the usual amount of water and cook.
Put the freshly cooked hot rice in a large bowl. Sprinkle in the combined sushi vinegar ingredients and mix together using a cutting motion. Cover with a moist wrung-out kitchen towel, and leave to cool to body temperature.
Cover the makisu with plastic wrap and spread the rice. Place nori seaweed underneath the wrap for eye-measurement.
Lay the shiso leaves, avocado, boiled shrimp (sliced lengthwise), and leek on the edge closest to you.
Roll up gently and not too tightly.
Sprinkle some sesame seeds on the cutting board. Remove the plastic wrap from the rolls made in Step 5 and roll over the board to coat the surface with sesame seeds.
Slice and it's done. You could also squirt mayonnaise on top.
Story Behind this Recipe
I used leftover sushi rice from the 'Ehoumaki' (sushi rolls eaten at Setsubun) to make these inside-out sushi.
If you lay out the nori sheet underneath the plastic wrap, it will give you a good idea of how to spread the rice. The key is to avoid rolling too tightly, otherwise the rice grains will mush together. Try with imitation crab sticks if you don't have shrimp.