Beat the sugar with the butter until pale and creamy. Add the egg, flour, ground pistachios, ground coriander seeds and 1/2 tsp salt and beat to a smooth paste. Put in a piping bag or cover with cling film and chill in the fridge for 2 hrs.
Heat oven to 160C/140C fan/gas 3 and line two large baking sheets with baking parchment. Pipe (or spoon) 5cm lengths about 1.5 cm wide onto the paper, leaving a few cm between each biscuit. Garnish with the chopped pistachios and whole coriander seeds and bake for 10-15 mins until golden at the edges. Turn off the oven and leave the biscuits inside for 20-30 mins, then remove and leave for 5-10 mins until so crisp they slide off the sheet. Cool fully before serving. Try pairing with our strawberry labneh, or you can keep in an airtight container for 2-3 days.