Pre-heat the oven to 180C, 350F, gas mark 4
Scatter the kale over a baking tray, sprinkle over the cumin seeds if using and then a couple of sprays of the rapeseed oil and season with a little salt.
Bake in the oven for 9-10 minutes, or until they have just gone crispy. Be careful as they will burn very quickly if you don't watch them.
Remove from the oven, allow to cool. These will keep in an airtight container for 24 hours.