Simply place raw, unsalted and shelled pistachios in the bowl of your food processor. Pulse until you get a powder - more or less coarse depending on the texture you are after. Make sure not to over-mix or the pistachios will start releasing oil and eventually turn into a paste. Optionally, you can toast the nuts in the oven for 5 to 10 minutes to boost their flavour. You will get a darker brown pistachio flour with a stronger nutty flavour.