1: Preheat the oven to 150°C (300°F). Spread 100 g pistachios out over a baking sheet (set aside about 30 for decoration) and put in the oven for 15 minutes to roast them. Leave to cool then blend briefly to a coarse texture. You can also chop them quickly with a knife.
2: Put 250 g flour, 125 g butter, 125 g caster sugar and 1 Egg into a food-mixer bowl. Knead on slow speed until the dough is smooth and evenly mixed.
3: Add 50 g Pistachio powder or paste and the chopped pistachios. Knead for a further 1 or 2 minutes to mix well.
4: Gather the dough into a large flat cake, wrap in stretch plastic film and put in the fridge for at least 2 hours (the dough can be prepared the day before you want to use it and left overnight).
5: Preheat the oven to 180°C (360°F). Roll out the dough using a rolling pin to about ½ cm ( ¼ inch)and cut out small circles of dough with a cutter (the easiest way).
6: You can use a different shape of cutter. The one I am using here is traditionally used for calissons. Place a whole pistachio on the top and press in gently. Bake for around 20 minutes.
Remarks
To bring out the pistachio flavour even more, you can add a drop of pistachio essence to the dough, but this is not essential. As usual with shortbread-style biscuits, do be careful not to overcook them.