Wash the yuzu skin well and zest with a microplane or zester. You can also use a knife to carefully slice off the peel, then cut into small pieces. Try not to get any of the white part underneath the skin as it's a bit bitter.

Chop up the green chilis and add all ingredients to a mortar & pestle (Japanese suribachi if you have it) or a small food processor. Using a mortar & pestle will bring out the fragrance and flavor of the citrus a bit better.

Grind or process until you have a yellow-ish green paste.

Scrap into a glass jar (don't use plastic or metal because the yuzu kosho could pick up unwanted flavors).

Cover with a bit of plastic wrap and put on the lid. Store in the fridge for several months. It's quite salty and spicy so you only need to use a little at a time!