Make sure the chilies and the blender parts are all very dry before starting.
Remove the seeds and stems by cutting off the top of the chilies with sharp scissors and emptying out them out.
Seal the blender lid very well and blend on low speed. Gradually increase to high speed and blend for about 1 minute.
Turn off the machine and wait 1-2 minutes for the dust to settle. (Get ready to sneeze!)
Use a spatula to carefully remove the powder from the blender. There will be a large amount of powder stuck to the lid of the blender that you won’t want to miss.
Keep in a sealed container, in a cool dark place for up to 3 months for maximum flavour.